As filed with the Securities and Exchange Commission on June 27, 2022

Registration Statement No. 333-      ​

UNITED STATES SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM S-4

REGISTRATION STATEMENT
UNDER THE SECURITIES ACT OF 1933

BROOKLINE BANCORP, INC.

(Exact name of registrant as specified in its charter)

Delaware (State or other jurisdiction of
incorporation or organization) 6022 (Primary Standard Industrial
Classification Code Number) 04-3402944 (I.R.S. Employer
Identification Number)

131 Clarendon Street,
Boston, Massachusetts 02116
(617) 425-4600

(Address, including zip code, and telephone number, including area code, of registrant’s principal executive offices)

Paul A. Perrault
Chief Executive Officer
131 Clarendon Street
Boston, Massachusetts 02116
(617) 425-4600

(Name, address, including zip code, and telephone number, including area code, of agent for service)

Copies to:

Samantha M. Kirby, Esq.
Goodwin Procter LLP
100 Northern Avenue
Boston, Massachusetts 02210
(617) 570-1000 Marissa Martin, Esq.
Brookline Bancorp, Inc.
131 Clarendon Street
Boston, Massachusetts 02116
(617) 425-4600 Kip A. Weissman, Esq.
Luse Gorman, PC
5335 Wisconsin Avenue, N.W.
Suite 780
Washington, DC 20015
(202) 274-2000

Approximate date of commencement of proposed sale of the securities to the public: As soon as practicable after this registration statement becomes effective and upon completion of the merger described in this registration statement.

If the securities being registered on this Form are being offered in connection with the formation of a holding company and there is compliance with General Instruction G, check the following box. □

If this Form is filed to register additional securities for an offering pursuant to Rule 462(b) under the Securities Act, check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering. □

If this Form is a post-effective amendment filed pursuant to Rule 462(d) under the Securities Act, check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering. □

Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer, a smaller reporting company or an emerging growth company. See the definitions of “large accelerated filer,” “accelerated filer,” “smaller reporting company,” and “emerging growth company” in Rule 12b-2 of the Exchange Act.

Large accelerated filer ☒	Accelerated filer ☐
Non-accelerated filer ☐	Smaller reporting company ☐
​	Emerging growth company ☐

If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 7(a)(2)(B) of the Securities Act. ☐

If applicable, place an X in the box to designate the appropriate rule provision relied upon in conducting this transaction:

Exchange Act Rule 13e-4(i) (Cross-Border Issuer Tender Offer) ☐

Exchange Act Rule 14d-1(d) (Cross-Border Third-Party Tender Offer) ☐

The registrant hereby amends this registration statement on such date or dates as may be necessary to delay its effective date until the registrant shall file a further amendment which specifically states that this registration statement shall thereafter become effective in accordance with Section 8(a) of the Securities Act of 1933 or until the registration statement shall become effective on such date as the Commission, acting pursuant to said Section 8(a), may determine.

The information in this proxy statement/prospectus is not complete and may be changed or supplemented. We may not sell these securities until the registration statement filed with the Securities and Exchange Commission is effective. This proxy statement/prospectus is not an offer to sell these securities and it is not soliciting an offer to buy these securities in any state where the offer or sale is not permitted.

Subject to Completion, dated June 27, 2022

MERGER PROPOSED — YOUR VOTE IS VERY IMPORTANT

Dear Fellow PCSB Financial Corporation Stockholder:

On May 23, 2022, PCSB Financial Corporation (“PCSB”) and Brookline Bancorp, Inc. (“Brookline”) entered into an Agreement and Plan of Merger, which we refer to as the “merger agreement,” pursuant to which PCSB will merge with and into Brookline, which we refer to as the “merger,” with Brookline surviving the merger as the surviving corporation. Following the completion of the merger, PCSB Bank, PCSB’s banking subsidiary, will become a subsidiary of Brookline. If the merger is completed, PCSB’s stockholders as of the completion of the merger will be entitled to receive, for each share of PCSB common stock owned, at their election, $22.00 in cash, which we refer to as the “cash consideration,” or 1.3284 shares of Brookline common stock, which we refer to as the “stock consideration,” and collectively with the cash consideration, the “merger consideration.” The ability for a PCSB stockholder to elect either the cash consideration or the stock consideration is subject to allocation procedures to ensure that 60% of the outstanding shares of PCSB common stock will be converted to Brookline common stock. Based on the number of shares of PCSB common stock and Brookline common stock outstanding on [•], 2022, we expect that the delivery of the stock consideration will require Brookline to issue approximately [•] shares of Brookline common stock in connection with the merger, and that holders of shares of PCSB common stock immediately prior to the closing of the merger will hold, in the aggregate, approximately [•]% of the issued and outstanding shares of Brookline common stock immediately following the closing of the merger (without giving effect to any shares of Brookline common stock held by PCSB stockholders prior to the merger).

Based on the closing stock price of Brookline common stock on the Nasdaq Global Select, which we refer to as the “Nasdaq,” on May 23, 2022, the last full trading day before the date of the public announcement of the merger, of $14.96, and the exchange ratio of 1.3284, the value of the stock consideration would be $20.72 for each share of PCSB common stock, as of [•], 2022. Based on the closing stock price of Brookline common stock on the Nasdaq on [•], 2022, the latest practicable date before the date of this proxy statement/ prospectus, of $[•], and the exchange ratio of 1.3284, the value of the stock consideration would be $[•] for each share of PCSB common stock, as of such date.

The market prices of both Brookline common stock and PCSB common stock will fluctuate before the completion of the merger. You should obtain current stock price quotations for Brookline common stock and PCSB common stock before you vote. Brookline common stock is quoted on the Nasdaq under the symbol “BRKL.” PCSB common stock is quoted on the Nasdaq Capital Markets under the symbol “PCSB.”

The merger cannot be completed unless the merger agreement and merger are approved by the affirmative vote of at least a majority (50%) of the outstanding shares of PCSB common stock entitled to vote thereon.

The special meeting of stockholders of PCSB Financial Corporation will be held at our executive offices/headquarters at 2651 Strang Boulevard, Suite 100, Yorktown Heights, New York on [•], 2022 at [•], local time.

PCSB stockholders of record as of the close of business on [•], 2022, the record date for the special meeting, are entitled to notice of, and to vote at, the special meeting.

Your vote is very important, regardless of the number of shares of PCSB common stock you own. To ensure your representation at the PCSB special meeting, please take time to vote by following the instructions contained in this proxy statement/prospectus and on your proxy card. Please vote promptly whether or not you expect to attend the PCSB special meeting. Submitting a proxy now will not prevent you from being able to vote at the PCSB special meeting. We cannot complete the transactions contemplated by the merger agreement unless PCSB stockholders approve the merger agreement and merger. The affirmative vote of a majority of the outstanding shares of PCSB common stock is required to approve the merger agreement and merger.

PCSB’s board of directors unanimously recommends that PCSB stockholders vote “FOR” the proposal to approve the merger agreement and “FOR” the other matters to be considered at the PCSB special meeting. In considering the recommendation of the board of directors of PCSB, you should be aware that certain directors and executive officers of PCSB may have interests in the merger that are different from, or in addition to, the interests of PCSB stockholders generally. See the section entitled “The Merger — Interests of PCSB’s Directors and Executive Officers in the Merger” beginning on page [•] of the accompanying proxy statement/​prospectus.

The accompanying proxy statement/prospectus describes the special meeting of PCSB stockholders, the merger, the documents relating to the merger and other related matters. Please read carefully the entire proxy statement/ prospectus, including the section entitled “Risk Factors” beginning on page 18, for a discussion of the risks relating to the proposed merger, and the annexes and documents incorporated by reference into the proxy statement/prospectus.

If you have any questions regarding the accompanying proxy statement/prospectus, you may contact Laurel Hill Advisory Group, LLC, PCSB’s proxy solicitor, by calling toll-free at [•].

Sincerely,

Joseph D. Roberto
Chairman, President and Chief Executive Officer

NEITHER THE SECURITIES AND EXCHANGE COMMISSION NOR ANY STATE SECURITIES COMMISSION HAS APPROVED OR DISAPPROVED THE MERGER OR OTHER TRANSACTIONS DESCRIBED IN THE ACCOMPANYING PROXY STATEMENT/PROSPECTUS OR THE SECURITIES TO BE ISSUED PURSUANT TO THE MERGER UNDER THE ACCOMPANYING PROXY STATEMENT/PROSPECTUS NOR HAVE THEY DETERMINED IF THE ACCOMPANYING PROXY STATEMENT/PROSPECTUS IS ACCURATE OR ADEQUATE. ANY REPRESENTATION TO THE CONTRARY IS A CRIMINAL OFFENSE.

The securities to be issued in connection with the merger are not savings accounts, deposits or other obligations of any bank or savings association and are not insured by the Federal Deposit Insurance Corporation or any other governmental agency.

The accompanying proxy statement/prospectus is dated [•], 2022 and is first being mailed to PCSB stockholders on or about [•], 2022.

PCSB FINANCIAL CORPORATION
2651 Strang Blvd., Suite 100
Yorktown Heights, NY 10598
(914) 248-7272

NOTICE OF 2022 SPECIAL MEETING OF STOCKHOLDERS

TIME AND DATE	[•], local time, on [•], 2022.
PLACE	2651 Strang Blvd., Suite 100, Yorktown Heights, New York.
BUSINESS ITEMS	(1) To approve and adopt the Agreement and Plan of Merger, dated as of May 23, 2022 (the “merger agreement”), by and between Brookline Bancorp, Inc. (“Brookline”) and PCSB Financial Corporation (“PCSB”), and to approve the transactions contemplated by the merger agreement (the “merger,” with such proposal the “PCSB merger proposal”);
​	(2) to approve a non-binding, advisory proposal to approve the compensation payable to the named executive officers of PCSB in connection with the merger (the “PCSB compensation proposal”); and
​	(3) to approve the adjournment of the PCSB special meeting, if necessary or appropriate, to solicit additional proxies if there are insufficient votes at the time of the PCSB special meeting to approve the PCSB merger proposal, or to ensure that any supplement or amendment to the accompanying proxy statement/prospectus is timely provided to PCSB stockholders (the “PCSB adjournment proposal”).
RECORD DATE	The board of directors of PCSB has fixed the close of business on [•], 2022 as the record date for the PCSB special meeting. Only holders of record of PCSB common stock as of the close of business on the record date for the PCSB special meeting are entitled to notice of the PCSB special meeting or any adjournment or postponement thereof. Only holders of record of PCSB common stock are entitled to vote at the PCSB special meeting or any adjournment or postponement thereof.
PROXY VOTING	It is important that your shares be represented and voted at the meeting. You can vote your shares via the Internet, by telephone or by completing and returning the proxy card or voting instruction card sent to you. You can revoke your proxy at any time before its exercise at the meeting by following the instructions in the proxy statement.
NO APPRAISAL RIGHTS	Under Maryland law, PCSB common stockholders do not have appraisal rights.
BOARD RECOMMENDATIONS	The PCSB board of directors unanimously recommends that PCSB stockholders vote “FOR” the PCSB merger proposal, “FOR” the PCSB compensation proposal and “FOR” the PCSB adjournment proposal.

By Order of the Board of Directors,

Clifford S. Weber
Corporate Secretary

Yorktown Heights, New York
[•], 2022

ADDITIONAL INFORMATION

This proxy statement/prospectus incorporates important business and financial information about PCSB and Brookline from other documents that PCSB and Brookline have filed with the U.S. Securities and Exchange Commission (the “SEC”) and that are contained in or incorporated by reference into this proxy statement/prospectus. For a listing of documents incorporated by reference into this proxy statement/​prospectus, please see the section entitled “Where You Can Find More Information” beginning on page [•] of this proxy statement/prospectus. This information is available for you to review through the SEC’s website at www.sec.gov.

You may request copies of this proxy statement/prospectus and any of the documents incorporated by reference into this proxy statement/prospectus or other information concerning PCSB, without charge, by telephone or written request directed to:

PCSB Financial Corporation
2651 Strang Boulevard, Suite 100
Yorktown Heights, New York 10598
(914) 248-7272
Attention: Investor Relations

You may also request a copy of this proxy statement/prospectus and any of the documents incorporated by reference into this proxy statement/prospectus or other information concerning Brookline, without charge, by telephone or written request directed to:

Brookline Bancorp, Inc.
131 Clarendon Street
Boston, Massachusetts 02116
(617) 425-4600
Attn: Carl M. Carlson

In order for you to receive timely delivery of the documents in advance of the special meeting of PCSB stockholders to be held on [•], 2022, your request for such information must be received no later than five business days prior to the date of the special meeting, by [•], 2022.

The proxy statement/prospectus is also available on Investor Relations tab of PCSB’s website at www.pcsb.com. The information on PCSB’s website is not part of this proxy statement/prospectus. References to PCSB’s website in this proxy statement/prospectus are intended to serve as textual references.

ABOUT THIS PROXY STATEMENT/PROSPECTUS

This document, which forms part of a registration statement on Form S-4 filed with the SEC by Brookline (File No. 333-[•]), constitutes a prospectus of Brookline under Section 5 of the Securities Act of 1933, as amended (the “Securities Act”) with respect to the shares of common stock, par value $0.01 per share, of Brookline (“Brookline common stock”) to be issued to PCSB stockholders pursuant to the merger agreement. This document also constitutes a proxy statement of PCSB under Section 14(a) of the Securities Exchange Act of 1934, as amended (the “Exchange Act”). It also constitutes a notice of meeting with respect to the special meeting, at which PCSB stockholders will be asked to consider and vote upon the approval of the merger agreement.

Brookline has supplied all information contained or incorporated by reference into this proxy statement/​prospectus relating to Brookline, and PCSB has supplied all information contained or incorporated by reference into this proxy statement/prospectus relating to PCSB.

Brookline and PCSB have not authorized anyone to provide you with information that is different from or in addition to that contained in or incorporated by reference into this proxy statement/prospectus. Brookline and PCSB do not take any responsibility for, or provide any assurance as to the reliability of, any other information others may give you. This proxy statement/prospectus is dated [•], 2022, and you should not assume that the information contained in this proxy statement/prospectus is accurate as of any date other than such date. Further, you should not assume that the information incorporated by reference into this proxy statement/prospectus is accurate as of any date other than the date of the incorporated document. Neither the mailing of this proxy statement/prospectus to PCSB stockholders nor the issuance by Brookline of shares of its common stock pursuant to the merger agreement will create any implication to the contrary.

TABLE OF CONTENTS

​	Page
QUESTIONS AND ANSWERS ABOUT THE MERGER AND THE SPECIAL MEETING	​	1
BROOKLINE MARKET PRICE AND DIVIDEND INFORMATION	​	6
SUMMARY	​	7
The Companies	​	7
The PCSB Special Meeting	​	8
The Merger	​	9
RISK FACTORS	​	18
CAUTIONARY STATEMENT CONCERNING FORWARD-LOOKING INFORMATION	​	23
UNAUDITED PRO FORMA CONDENSED COMBINED FINANCIAL INFORMATION	​	25
THE COMPANIES	​	32
Brookline	​	32
PCSB	​	32
THE PCSB SPECIAL MEETING	​	33
Date, Time and Place of the Meeting	​	33
Who Can Vote and Quorum	​	33
Vote Required; Treatment of Abstentions and Failure to Vote	​	34
Ownership of PCSB Shares, Attending the PCSB Special Meeting	​	34
ESOP and 401(k) Plan Participant Voting	​	35
Proxies	​	35
Voting by Proxy	​	36
Revocability of Proxies	​	36
Delivery of Proxy Materials	​	36
Solicitation of Proxies	​	37
Other Matters to Come Before the PCSB Special Meeting	​	37
Appraisal Rights	​	37
PROPOSAL NO. 1 – PCSB MERGER PROPOSAL	​	38
General	​	38
Background of the Merger	​	38
Reasons for the Merger	​	42
Recommendation of the PCSB Board of Directors	​	44
Opinion of PCSB’s Financial Advisor	​	44
Certain Unaudited Financial Information	​	55
Brookline’s Reasons for the Merger	​	58
Accounting Treatment	​	59
Post-Closing Capitalization	​	59
Listing of Brookline Common Stock to be Issued in the Merger	​	59
Number of Holders of Common Stock and Number of Shares Outstanding	​	60
Interests of PCSB Directors and Executive Officers in the Merger	​	60
Golden Parachute Compensation	​	67
THE MERGER AGREEMENT	​	69
Structure of the Merger	​	69
Closing of the Merger	​	69
Boards of Directors of the Surviving Corporation	​	69

​	Page
Merger Consideration	​	69
Election Procedures	​	70
Allocation Procedures	​	70
Exchange of PCSB Stock Certificates for Brookline Common Stock	​	73
Treatment of PCSB Stock Options	​	74
Treatment of PCSB Restricted Stock	​	74
Conditions to the Merger	​	74
No Solicitation	​	77
Termination	​	78
Termination Fee	​	80
Nasdaq Listing	​	81
Indemnification and Insurance	​	81
Conduct of Business Pending the Merger	​	81
Employee Benefits	​	84
Other Covenants	​	85
Representations and Warranties	​	85
Expenses	​	87
Waiver / Amendments	​	87
Regulatory Approvals Required for the Merger	​	87
THE VOTING AGREEMENTS	​	89
MATERIAL UNITED STATES FEDERAL INCOME TAX CONSEQUENCES OF THE MERGER	​	90
Tax Consequences of the Merger	​	91
Receipt of Solely Brookline Common Stock	​	91
Receipt of Solely Cash	​	91
Receipt of Brookline Common Stock and Cash	​	92
Cash in Lieu of Fractional Shares	​	92
Tax Opinions	​	92
Information Reporting and Backup Withholding	​	93
Other Tax Consequences	​	93
DESCRIPTION OF BROOKLINE’S CAPITAL STOCK	​	94
COMPARISON OF STOCKHOLDER RIGHTS	​	95
PROPOSAL NO. 2 – PCSB COMPENSATION PROPOSAL	​	102
PROPOSAL NO. 3 – PCSB ADJOURNMENT PROPOSAL	​	103
LEGAL MATTERS	​	104
EXPERTS	​	104
FUTURE STOCKHOLDER PROPOSALS	​	104
WHERE YOU CAN FIND MORE INFORMATION	​	105
MISCELLANEOUS	​	107
Annex A – Merger Agreement	​	A-1
Annex B – Opinion of Piper Sandler & Co.	​	B-1

QUESTIONS AND ANSWERS ABOUT THE MERGER AND THE PCSB SPECIAL MEETING

The following questions and answers are intended to address briefly some commonly asked questions regarding the merger and the PCSB special meeting. These questions and answers may not address all questions that may be important to you as a stockholder. To more fully understand the merger and the PCSB special meeting, you should read this entire proxy statement/prospectus, including the materials attached as annexes, as well as the documents that have been incorporated by reference into this proxy statement/​prospectus.

In this proxy statement/prospectus, unless the context otherwise requires:

•

“Brookline” refers to Brookline Bancorp, Inc., a Delaware corporation;

•

“Brookline’s bylaws” refers to the amended and restated bylaws of Brookline;

•

“Brookline’s charter” refers to the certificate of incorporation of Brookline;

•

“Brookline common stock” refers to the common stock of Brookline, par value $0.01 per share;

•

“merger” refers to the merger of PCSB with and into Brookline, with Brookline as the surviving corporation;

•

“merger agreement” refers to the Agreement and Plan of Merger by and between Brookline and PCSB, dated as of May 23, 2022;

•

“PCSB” refers to PCSB Financial Corporation, a Maryland corporation;

•

“PCSB’s bylaws” refers to the amended and restated bylaws of PCSB;

•

“PCSB’s charter” refers to the articles of incorporation of PCSB;

•

“PCSB common stock” refers to the common stock of PCSB, par value $0.01 per share;

•

“PCSB special meeting” refers to the special meeting of PCSB stockholders to be held on [•], 2022, at [•] local time, at [•]; and

•

“we,” “us” and “our” refer collectively to PCSB and Brookline.

Q.

Why am I receiving this proxy statement/prospectus?

A.

You are being asked to approve the merger of PCSB with and into Brookline, with Brookline as the surviving corporation, pursuant to the terms of the merger agreement that is described in this proxy statement/prospectus. A copy of the merger agreement is attached to this proxy statement/prospectus as Annex A.

In order to complete the merger, PCSB stockholders must vote to approve the merger. PCSB will hold the PCSB special meeting to obtain this required approval. This proxy statement/prospectus contains important information about the merger, the merger agreement, the PCSB special meeting, and other related matters, and you should read it carefully. The enclosed voting materials for the PCSB special meeting allow you to vote your shares of PCSB common stock without attending the PCSB special meeting.

We are delivering this proxy statement/prospectus to you as the proxy statement for the PCSB special meeting and the prospectus for the shares of Brookline common stock to be issued in connection with the merger. It is a proxy statement because PCSB’s board of directors is soliciting proxies from stockholders to vote on the approval and adoption of the merger agreement, and your proxy will be used at the PCSB special meeting or at any adjournment or postponement of the PCSB special meeting. It is a prospectus because Brookline will issue Brookline common stock to PCSB stockholders who receive stock consideration in the merger, and this prospectus contains information about Brookline common stock.

1

Q.

What do I need to do now?

A.

You should carefully read and consider the information contained or incorporated by reference into this proxy statement/prospectus, including its annexes. This proxy statement/prospectus contains important information about the merger, the merger agreement, Brookline and PCSB. After you have read and considered this information, PCSB stockholders are requested to submit a proxy by one of the methods described above in advance of the PCSB special meeting. Whether or not you plan to attend the PCSB special meeting in person, you are encouraged to vote as soon as possible so that your shares of common stock will be represented and voted at the PCSB special meeting. The proxy card will instruct the persons named on the proxy card to vote your shares at the PCSB special meeting as you direct. If you sign, date and send in a proxy card and do not indicate how you wish to vote, the proxy will be voted “FOR” approval and adoption of the merger agreement, “FOR” approval, on a non-binding advisory basis, of the merger-related named executive officer compensation, and, if necessary and appropriate, “FOR” the PCSB adjournment proposal.

Q.

Who can vote at the PCSB special meeting? (page [•])

A.

Holders of record of PCSB common stock at the close of business on [•], which is the record date for the PCSB special meeting, are entitled to vote at the PCSB special meeting.

Q.

What is the difference between holding shares as a stockholder of record and as a beneficial owner of shares held in “street name”?

A.

If your shares are registered directly in your name with our transfer agent, [•], you are considered the stockholder of record with respect to those shares. As a stockholder of record, you may vote at the PCSB special meeting or vote by proxy by one of the methods described below. If your shares are held in an account by a bank, broker or other nominee (the record holder of your shares), then you are the beneficial owner of shares held in “street name.” As the beneficial owner, you have the right to direct your record holder how to vote your shares of common stock, and the record holder is required to vote your shares of common stock in accordance with your instructions.

Q.

How may I vote my shares for the PCSB special meeting proposals presented in this proxy statement/​prospectus? (page [•])

A.

PCSB is sending you this proxy statement to request that you allow your shares of PCSB common stock to be represented at the PCSB special meeting by the persons named in the enclosed proxy card. All shares of PCSB common stock represented at the meeting by properly executed and dated proxies will be voted according to the instructions indicated on the proxy card. If you sign, date and return a proxy card without giving voting instructions, your shares will be voted as recommended by the Board of Directors.

Instead of voting by completing and mailing a proxy card, registered stockholders can vote their shares of PCSB common stock via the Internet or by telephone. The Internet and telephone voting procedures are designed to authenticate stockholders’ identities, allow stockholders to provide their voting instructions and confirm that their instructions have been recorded properly. Specific instructions for Internet and telephone voting appear on the enclosed proxy card and for the benefit plans on the voting instruction cards. The deadline for Internet and telephone voting is [•], on [•], 2022.

Q.

If my shares are held in “street name” by my broker, bank or other nominee, will my broker, bank or other nominee automatically vote my shares for me? (page [•])

A.

No. Your broker, bank or other nominee will not vote your shares unless you provide instructions to your broker, bank or other nominee on how to vote. It is important that you provide timely instruction to your broker or bank to ensure that all shares of PCSB common stock that are voted at the PCSB special meeting. You should follow the vote instruction form sent to you by your broker, bank or other nominee with this proxy statement/prospectus explaining how you can vote.

2

Q.

What if I fail to submit a proxy or to instruct my broker, bank or other nominee to vote my shares? (page [•])

A.

If you fail to submit a proxy or to instruct your broker, bank or other nominee to vote your shares, your shares will not be voted. This will have the same effect as a vote against the proposals

Q.

What should I do if I receive more than one set of voting materials?

A.

You may receive more than one set of voting materials, including multiple copies of this proxy statement/​prospectus and multiple proxy cards or voting instruction cards. For example, if you hold your PCSB shares in more than one brokerage account, you will receive a separate voting instruction card for each brokerage account in which you hold PCSB shares. Please complete, sign, date and return each proxy card and voting instruction card that you receive, or otherwise follow the voting instructions set forth on the proxy card and voting instruction card

Q.

Can I change my vote after I have submitted a proxy? (page [•])

A.

Yes. If you directly hold shares of PCSB common stock in your name as a record holder, you can change your proxy vote at any time before your proxy is voted at the PCSB special meeting. You can do this by:

•

submitting a written statement that you would like to revoke your proxy to the corporate secretary of PCSB;

•

signing and returning a proxy card with a later date;

•

attending the PCSB special meeting and voting at the PCSB special meeting; or

•

voting by telephone or the Internet at a later time.

If you hold your shares in “street name” through a bank, broker, trustee or nominee and you have instructed the bank, broker, trustee or nominee to vote your shares, you must follow the directions received from your bank, broker, trustee or nominee to change those instructions

Q.

What happens if I sell my shares after the record date but before the PCSB special meeting?

A.

The record date for the PCSB special meeting is earlier than both the date of the PCSB special meeting and the date that the merger is expected to be completed. If you are a PCSB stockholder and you sell or otherwise transfer your PCSB shares after the record date but before the date of the PCSB special meeting, you will retain your right to vote at the PCSB special meeting, but you will transfer the right to receive the merger consideration to the person to whom you transferred your shares. In order to receive the merger consideration, you must hold your shares through completion of the merger

Q

What will PCSB stockholders receive in the merger? (page [•])

A.

If the merger agreement is approved and adoption by the holders of at least a majority of the shares of PCSB common stock outstanding and entitled to vote on the matter at the PCSB special meeting and the merger is subsequently completed, each outstanding share of PCSB common stock will be converted into the right to receive, subject to the terms and conditions of the merger agreement (including allocation procedures), at the election of the holder thereof, the following consideration: (i) $22.00 in cash or (ii) 1.3284 shares of Brookline common stock, plus cash in lieu of fractional shares. The allocation procedures included in the merger agreement are intended to ensure that 60% of the total number of shares of PCSB common stock outstanding immediately prior to the effective time of the merger will be converted into shares of Brookline common stock, and the remaining shares of PCSB common stock will be converted into cash.

3

Q.

Will PCSB stockholders receive any fractional share of Brookline common stock as part of the merger consideration? (page [•])

A.

No. Brookline will not issue any fractional shares of Brookline common stock in the merger. Instead, Brookline will pay you the cash value of a fractional share measured by the 10-day average stock price of Brookline common stock as reported on Nasdaq stock market (“Nasdaq”) for the ten consecutive trading day period ending on the fifth business day prior to the closing date, rounded to the nearest whole cent.

Q.

How do PCSB stockholders make an election as to the form of merger consideration they wish to receive? (page [•])

A.

An election form and other appropriate and customary transmittal materials will be mailed no less than 20 business days prior to the anticipated closing date of the merger (or such other date as PCSB and Brookline mutually agree) to each holder of record of PCSB common stock as of five business days prior to such mailing date. Each election form will permit the holder of record of PCSB common stock (or the beneficial owner through proper instructions and documentation) to elect to receive either (i) $22.00 in cash or (ii) 1.3284 shares of Brookline common stock, plus cash in lieu of fractional shares. You will also receive detailed instructions describing the procedures you must follow to make your election.

We are not making any recommendation to you as to whether you should elect to receive cash or shares of Brookline common stock in the merger. You should evaluate your own specific circumstances and investment preferences in making your election

Q.

Can PCSB stockholders elect to receive the merger consideration in the form of cash with respect to a portion of their PCSB shares and Brookline common stock with respect to the rest of their PCSB shares? (page [•])

A.

The election form and letter of transmittal will permit you, subject to the allocation procedures described in this proxy statement/prospectus, to receive at your election:

•

all of your merger consideration in the form of cash;

•

all of your merger consideration in the form of shares of Brookline common stock; or

•

a portion of your merger consideration in cash and the remaining portion in shares of Brookline common stock.

Q.

Will PCSB stockholders receive the form of consideration they elect? (page [•])

A.

The form of merger consideration you actually receive may differ from the form of consideration that you elect to receive. This is because the consideration to be received by each PCSB stockholder is subject to allocation procedures to ensure that 60% of total number of shares of PCSB common stock outstanding immediately prior to the effective time of the merger will be converted into shares of Brookline common stock, and the remaining shares of PCSB common stock will be converted into cash

Q.

Do PCSB stockholders have the right to dissent and obtain the fair market value of their shares? (page [•])

A.

No. Pursuant to Maryland law, PCSB stockholders do not have appraisal rights with respect to the merger

Q.

Should PCSB stockholders send in their stock certificates now? (page [•])

A.

No. You will receive separate written instructions for surrendering your shares of PCSB common stock in exchange for the merger consideration. In the meantime, you should retain your stock certificate(s) because they are still valid. Please do not send in your stock certificate(s) with your proxy card.

4

Q.

Where can I find more information about Brookline?

A.

You can find more information about Brookline from the various sources described in the section of this proxy statement/prospectus titled “Where You Can Find More Information” beginning on page [•].

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BROOKLINE MARKET PRICE AND DIVIDEND INFORMATION

Brookline’s common stock currently trades on the Nasdaq Global Select Market under the symbol “BRKL.” On May 23, 2022, the last full trading day immediately preceding the public announcement of the merger, and on [•], 2022, the most recent practicable date prior to the mailing of this proxy statement/​prospectus, the last reported sales prices of Brookline’s common stock, as reported by the Nasdaq Global Select Market, were $14.96 per share and $[•] per share, respectively. The market price of Brookline common stock is likely to fluctuate prior to the effective time of the merger. You are encouraged to obtain current trading prices for Brookline’s common stock in considering whether to vote on the matters being considered at the annual meeting and in completing your election form for the merger consideration.

Brookline expects that after the completion of the merger, subject to approval and declaration by the Brookline board of directors, it will continue to declare quarterly cash dividends on shares of its common stock consistent with past practices. The actual payment of dividends is subject to numerous factors, and no assurance can be given that Brookline will pay dividends following the completion of the merger or that dividends will not be reduced in the future. The current annualized rate of distributions on the shares of Brookline common stock is $.52 per share.

As of [•], 2022, there were approximately [•] holders of record of Brookline’s common stock.

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SUMMARY

This summary highlights selected information from this proxy statement/prospectus and may not contain all of the information that is important to you. To more fully understand the merger and for a more complete description of the legal terms of the merger, you should read this entire document, including the annexes, as well as the other documents to which we have referred you. See the section of this proxy statement/prospectus titled “Where You Can Find More Information” beginning on page [•]. The page references in parentheses included in this summary will direct you to a more detailed description of each topic presented.

The Companies

Brookline (page [•])

Brookline Bancorp, Inc., a Delaware corporation, operates as a multi-bank holding company for Brookline Bank and its subsidiaries, Bank Rhode Island (“BankRI”) and its subsidiaries, Brookline Securities Corp. and Clarendon Private, LLC (“Clarendon Private”).

Brookline Bank, which includes its wholly owned subsidiaries, Longwood Securities Corp., First Ipswich Insurance Agency, and Eastern Funding LLC, operates 30 full-service banking offices and two lending offices in the greater Boston metropolitan area.

BankRI is headquartered in Providence, Rhode Island. BankRI, which includes its wholly owned subsidiaries, Acorn Insurance Agency, BRI Realty Corp. and BRI Investment Corp. and its wholly owned subsidiary, BRI MSC Corp., operates 20 full-service banking offices in the greater Providence, Rhode Island area.

As a commercially-focused financial institution with 50 full-service banking offices throughout greater Boston, the north shore of Massachusetts, and Rhode Island, Brookline, through Brookline Bank and BankRI, offers a wide range of commercial, business and retail banking services, including a full complement of cash management products, on-line banking services, consumer and residential loans and investment services, designed to meet the financial needs of small- to mid-sized businesses and individuals throughout central New England. Specialty lending activities including equipment financing are focused primarily in the New York and New Jersey metropolitan area. As full-service financial institutions, Brookline Bank and BankRI and their subsidiaries focus on the continued addition of well-qualified customers, the deepening of long-term banking relationships through a full complement of products and excellent customer service, and strong risk management. Clarendon Private is a registered investment advisor with the SEC. Through Clarendon Private, Brookline offers a wide range of wealth management services to individuals, families, endowments and foundations to help these clients meet their long-term financial goals.

The principal executive offices of Brookline are located at 131 Clarendon Street, Boston Massachusetts 02116, and the telephone number is (617) 425-4600.

PCSB (page [•])

PCSB is the bank holding company for PCSB Bank. On April 20, 2017, PCSB completed its initial public offering in connection with PCSB Bank’s conversion from a mutual savings bank to a stock savings bank. Other than holding the common stock of PCSB Bank, PCSB has not engaged in any significant business to date.

PCSB Bank is a New York-chartered commercial bank. PCSB Bank serves the banking needs of customers in the Lower Hudson Valley of New York State through its executive offices/headquarters and 14 banking offices located in Dutchess (two offices), Putnam (three offices), Rockland (one office) and Westchester (eight offices) Counties, New York. PCSB’s primary business activity is attracting deposits from the general public and using those funds primarily to originate and purchase commercial real estate loans, business loans and one- to four-family real estate loans and purchase investment securities.

PCSB’s primary market area encompasses all of Putnam and Westchester Counties and parts of Dutchess and Rockland Counties in New York, which are the counties in which its offices are located, and the surrounding areas.

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The principal executive offices of PCSB is located at 2651 Strang Blvd., Suite 100, Yorktown Heights, New York 10598, and its telephone number is (914) 248-7272.

The PCSB Special Meeting

Date, Time and Place of the PCSB Special Meeting (page [•])

The PCSB special meeting will be held on [•], 2022 at [•], local time, at PCSB’s headquarters, 2651 Strang Boulevard, Suite 100, Yorktown Heights, New York 10598.

Actions to be Taken at the PCSB Special Meeting (page [•])

At the PCSB special meeting, PCSB stockholders will be asked to consider and vote upon the following proposals:

•

the PCSB merger proposal;

•

the PCSB compensation proposal; and

•

the PCSB adjournment proposal.

Recommendation of the PCSB Board of Directors (page [•])

The PCSB board of directors recommends that you vote “FOR” the PCSB merger proposal, “FOR” the PCSB compensation proposal and “FOR” the PCSB adjournment proposal. See “The Merger — PCSB’s Reasons for the Merger; Recommendation of PCSB’s Board of Directors” beginning on page [•] for a more detailed discussion of the PCSB board of directors’ recommendation.

Record Date; Outstanding Shares; Shares Entitled to Vote (page [•])

The PCSB board of directors has fixed the close of business on [•], 2022 as the record date for determination of PCSB stockholders entitled to notice of and to vote at the PCSB special meeting. As of the record date, there were [•] shares of PCSB common stock outstanding and entitled to vote.

Quorum; Vote Required (page [•])

Holders of a majority of the outstanding shares of PCSB common stock entitled to vote at the PCSB special meeting must be present, either in attendance or by proxy, to constitute a quorum at the PCSB special meeting. If you fail to submit a proxy prior to the PCSB special meeting, or to vote at the PCSB special meeting, your shares of PCSB common stock will not be counted towards a quorum. Abstentions are considered present for the purpose of establishing a quorum but will not be counted as votes cast at the meeting.

Share Ownership of PCSB Management; Voting Agreements (page [•])

In connection with the merger agreement, PCSB’s directors and executive officers executed voting agreements with Brookline under which they agreed to vote their shares in favor of the agreement. As of [•], the record date for the PCSB special meeting, the directors and executive officers of PCSB may be deemed to be the beneficial owners of [•] shares of PCSB common stock, representing approximately [•]% of the outstanding shares of PCSB common stock.

Proxies, Voting and Revocation (page [•])

A holder of PCSB shares may vote by proxy or at the PCSB special meeting. If you hold your shares of PCSB common stock in your name as a record holder, to submit a proxy, you, as a holder of PCSB common stock, may use one of the following methods:

•

by telephone: by calling the toll-free number indicated on the accompanying proxy card and following the recorded instructions;

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•

through the Internet: by visiting the website indicated on the accompanying proxy card and following the instructions; or

•

by completing and returning the accompanying proxy card in the enclosed postage-paid envelope. The envelope requires no additional postage if mailed in the United States.

PCSB requests that PCSB stockholders vote by telephone, over the Internet or by completing and signing the accompanying proxy card and returning it to PCSB as soon as possible in the enclosed postage-paid envelope.

If you directly hold shares of PCSB common stock in your name as a record holder, you can change your proxy vote at any time before your proxy is voted at the PCSB special meeting. You can do this by:

•

submitting a written statement that you would like to revoke your proxy to the corporate secretary of PCSB;

•

signing and returning a proxy card with a later date;

•

attending the PCSB special meeting and voting at the PCSB special meeting; or

•

voting by telephone or the Internet at a later time.

If you hold your shares in “street name” through a bank, broker, trustee or nominee and you have instructed the bank, broker, trustee or nominee to vote your shares, you must follow the directions received from your bank, broker, trustee or nominee to change those instructions.

Appraisal Rights (page [•])

Under Maryland law, PCSB stockholders do not have appraisal rights with respect to the merger.

The Merger

Structure of the Merger (page [•])

Brookline and PCSB entered into the merger agreement on May 23, 2022. The merger agreement provides for the merger of PCSB with and into Brookline. The surviving corporation in the merger will be Brookline. Following the merger, PCSB Bank will operate as a wholly owned subsidiary of Brookline.

The merger will occur following approval of the proposal to approve and adopt the merger agreement by PCSB’s stockholders and satisfaction or waiver of all other conditions to the merger, including regulatory approvals. The merger agreement is attached to this document as Annex A. We encourage you to read the merger agreement in its entirety because it is the legal document that governs the merger.

Merger Consideration for PCSB Stockholders (page [•])

If the merger agreement is approved and adopted by the holders of at least a majority of the shares of PCSB common stock outstanding and entitled to vote on the matter at the PCSB special meeting and the merger is subsequently completed, each outstanding share of PCSB common stock will be converted into the right to receive, subject to the terms and conditions of the merger agreement (including allocation procedures), at the election of the holder thereof, either: (i) $22.00 in cash or (ii) 1.3284 shares of Brookline common stock, plus cash in lieu of fractional shares. The allocation procedures included in the merger agreement are intended to ensure that 60% of total number of shares of PCSB common stock outstanding immediately prior to the effective time of the merger will be converted into shares of Brookline common stock, and the remaining shares of PCSB common stock will be converted into cash.

No fractional shares of Brookline common stock will be issued in connection with the merger. Instead, each PCSB stockholder will receive an amount of cash, in lieu of any fractional share, based on the 10-day average stock price of Brookline common stock as reported on Nasdaq for the ten consecutive trading day period ending on the fifth business day prior to the closing date, rounded to the nearest whole cent.

Subject to the terms of the merger agreement, 60% of the merger consideration will be paid in the form of Brookline common stock. As of [•], 2022, there were [•] shares of PCSB common stock issued and

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outstanding and [•] shares of PCSB common stock reserved for issuance with respect to outstanding stock options. Based upon these numbers, assuming no exercise of outstanding stock options, this will result in current Brookline stockholders owning approximately [•]% of the combined company and PCSB stockholders owning approximately [•]% of the combined company.

Election Procedures for PCSB Stockholders (page [•])

An election form and other appropriate and customary transmittal materials will be mailed no less than 20 business days prior to the anticipated closing date or such other date as PCSB and Brookline agree to each holder of record of PCSB common stock as of five business days prior to such mailing date. Each election form will permit the holder of record of PCSB common stock (or the beneficial owner through proper instructions and documentation) to:

•

elect to receive $22.00 per share in cash, without interest, in exchange for all shares of PCSB common stock that you hold;

•

elect to receive 1.3284 shares of Brookline common stock in exchange for all shares of PCSB common stock that you hold;

•

elect to receive $22.00 per share in cash, without interest, with respect to a portion of the shares of PCSB common stock that you hold, and 1.3284 shares of Brookline common stock with respect to your remaining shares; or

•

make no election with respect to the consideration to be received by you in exchange for your shares of PCSB common stock.

You will have a limited period of time in which to complete the election form and return it as instructed. In order to be effective, a properly completed election form must be received by the exchange agent on or before 5:00 p.m., Eastern time, on the 25th day following the mailing date of the election form to PCSB stockholders, unless Brookline and PCSB mutually agree to another date and time as the election deadline, which date will be publicly announced by Brookline as soon as practicable prior to the election deadline. Those stockholders, if any, holding PCSB stock certificates will need to surrender your PCSB stock certificates to receive the appropriate consideration, but you should not send us any certificates now. You will receive detailed instructions on how to exchange your stock certificates along with your election form. If you do not submit an election form, you will receive instructions on where to surrender your PCSB stock certificates after the merger is completed.

If your shares or a portion of your shares of PCSB common stock are held in “street name” by a broker, bank or other nominee, an election form will be mailed to the broker, bank or other nominee with respect to those shares.

Allocation Procedures for PCSB Stockholders (page [•])

Your ability to elect to receive cash or shares of Brookline common stock in exchange for shares of PCSB common stock in the merger is subject to allocation procedures set forth in the merger agreement. Whether you receive the amount of cash and/or stock you request in your election form will depend in part on the elections of other PCSB stockholders. You may not receive the form of consideration that you elect in the merger, and you may instead receive a pro rata amount of cash and Brookline common stock.

If you have a preference for receiving either cash or Brookline common stock for your shares of PCSB common stock, you should return the election form indicating your preference. PCSB stockholders who make an election will be accorded priority over those stockholders who make no election in instances where the cash consideration or stock consideration must be re-allocated in order to achieve the required ratio of PCSB shares being converted into the right to receive cash and Brookline common stock. If you do not make an election, you will be allocated cash and/or Brookline common stock depending on the elections made by other PCSB stockholders. Please see the examples set forth in the section of this proxy statement/​prospectus titled “The Merger Agreement — Allocation Procedures” beginning on page [•]. However, even if you do make an election, the form of merger consideration you actually receive may differ from the form of merger consideration you elect to receive.

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Because the tax consequences of receiving cash will differ from the tax consequences of receiving Brookline common stock, you should carefully read the section of this proxy statement/prospectus titled “Material United States Federal Income Tax Consequences of the Merger” beginning on page [•].

Treatment of PCSB Stock Options (page [•])

At the effective time of the merger, each outstanding option to purchase PCSB common stock, whether vested or unvested, and which has not been previously exercised or canceled, will be automatically canceled and, on the closing date, PCSB shall pay to the holder thereof cash in an amount equal to the product of (i) the number of shares of PCSB common stock underlying such stock option (whether vested or unvested) and (ii) the excess, if any, of $22.00 per share over the exercise price per share of such stock option. The cash payment will be made without interest and will be net of all applicable withholding taxes. As of [•], 2022, there were outstanding [•] options to purchase shares of PCSB common stock.

Treatment of PCSB Restricted Stock (page [•])

As of immediately prior to the effective time of the merger, all restricted stock awards granted by PCSB will vest in full so as to no longer be subject to any forfeiture or vesting requirements, and all such shares of PCSB common stock shall be converted into the right to receive the merger consideration.

Opinion of PCSB’s Financial Advisor (page [•])

PCSB retained Piper Sandler & Co. (“Piper Sandler”) to act as financial advisor to PCSB’s board of directors in connection with PCSB’s consideration of a possible business combination. PCSB selected Piper Sandler to act as its financial advisor because Piper Sandler is a nationally recognized investment banking firm whose principal business specialty is financial institutions. In the ordinary course of its investment banking business, Piper Sandler is regularly engaged in the valuation of financial institutions and their securities in connection with mergers and acquisitions and other corporate transactions.

Piper Sandler acted as financial advisor to PCSB’s board of directors in connection with the proposed merger and participated in certain of the negotiations leading to the execution of the merger agreement. At the May 23, 2022 meeting at which PCSB’s board of directors considered the merger and the merger agreement, Piper Sandler delivered to the board of directors its oral opinion, which was subsequently confirmed in writing on May 23, 2022, to the effect that, as of such date, the merger consideration was fair to the holders of PCSB’s common stock from a financial point of view. The full text of Piper Sandler’s opinion is attached as Annex B to this proxy statement/prospectus. The opinion outlines the procedures followed, assumptions made, matters considered and qualifications and limitations on the review undertaken by Piper Sandler in rendering its opinion. The description of the opinion set forth below is qualified in its entirety by reference to the full text of the opinion. Holders of PCSB common stock are urged to read the entire opinion carefully in connection with their consideration of the proposed merger.

Interests of PCSB Directors and Executive Officers in the Merger (page [•])

In considering the recommendation of the board of directors of PCSB, PCSB’s stockholders should be aware that the directors and executive officers of PCSB have interests in the merger that are different from, or in addition to, the interests of PCSB’s other stockholders generally. The board of directors of PCSB was aware of these interests and considered them, among other matters, in approving the merger agreement and related transactions.

These interests include:

•

employment agreements with each of Joseph D. Roberto, Chairman, President and Chief Executive Officer of PCSB and PCSB Bank; Scott D. Nogles, Executive Vice President and Chief Operating Officer of PCSB and PCSB Bank; and Michael P. Goldrick, Executive Vice President and Chief Lending Officer of PCSB Bank, that provide for cash severance payments and continued non-taxable medical and dental insurance if the executive’s employment is voluntarily terminated for good reason or involuntarily terminated without cause following a change in control and during the term of the employment agreement;

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•

change in control agreements with each of Carol Bray, Senior Vice President and Chief Information Officer; Jeffrey Helf, Senior Vice President and Chief Financial Officer; Ruth Leser, Senior Vice President and Director of Human Resources; Michelle Nicholas, Senior Vice President, Chief Diversity Officer and Director of Community Development; Dominick Petramale, Senior Vice President and Chief Retail Officer, Director of Cash Management Services; Richard Petrone, Senior Vice President and Chief Credit Officer; and Clifford Weber, Senior Vice President, Chief Risk Officer and General Counsel, that provide for cash severance payments and continued non-taxable medical and dental insurance if the executive’s employment is voluntarily terminated for good reason or involuntarily terminated without cause following a change in control and during the term of the change in control agreement;

•

interests under supplemental retirement arrangements with each of Messrs. Roberto, Nogles and Goldrick, which will be paid in a lump sum to Messrs. Roberto, Nogles and Goldrick in connection with the merger;

•

the termination, accelerated vesting and payment of all outstanding PCSB stock options in an amount equal to $22.00 minus the exercise price of each option;

•

the acceleration of vesting of all outstanding PCSB restricted stock awards, which will be exchanged for the merger consideration;

•

interests under a director fee deferral plan with certain directors which will be paid in a lump sum in connection with the merger;

•

a consulting agreement that Brookline entered into with Mr. Roberto;

•

an employment agreement that Brookline and PCSB Bank entered into with Mr. Goldrick;

•

a member of the Board of Directors of PCSB Bank will be appointed as a director of Brookline and the remaining members of the Board of Directors of PCSB Bank will continue to serve on the Board of Directors of PCSB Bank immediately after the merger; and

•

the rights of PCSB officers and directors under the merger agreement to continued indemnification coverage and continued coverage under directors’ and officers’ liability insurance policies.

For a more complete description of these interests, see “The Merger — Interests of PCSB’s Directors and Executive Officers in the Merger.”

No Solicitation (page [•])

PCSB has agreed that neither it nor its subsidiaries and the respective officers, directors, employees, investment bankers, financial advisors, attorneys, accountants, consultants, affiliates and other agents of PCSB and its subsidiaries will directly or indirectly:

•

initiate, solicit, induce or knowingly encourage, or take any action to facilitate the making of, any inquiry, offer or proposal which constitutes, or could reasonably be expected to lead to, an acquisition proposal;

•

participate in any discussions or negotiations regarding any acquisition proposal or furnish, or otherwise afford access, to any person (other than Brookline) any information or data with respect to PCSB or any of its subsidiaries or otherwise relating to an acquisition proposal;

•

release any person from, waive any provisions of, or fail to enforce any confidentiality agreement or standstill agreement to which PCSB is a party; or

•

enter into any agreement, agreement in principle or letter of intent with respect to any acquisition proposal or approve or resolve to approve any acquisition proposal or any agreement, agreement in principle or letter of intent relating to an acquisition proposal.

However, PCSB is not prohibited from participating in any discussions or negotiations regarding any acquisition proposal or furnish, or otherwise afford access, to any person any information or data with respect to PCSB or any of its subsidiaries or otherwise relating to an acquisition proposal only if (i) PCSB has received a bona fide unsolicited written acquisition proposal that did not result from a breach of its non-solicit obligations; (ii) PCSB’s board of directors determines in good faith, after consultation with and

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having considered the advice of its outside legal counsel and its independent financial advisor, that (A) such acquisition proposal constitutes or is reasonably likely to lead to a superior proposal and (B) it is required to take such actions to comply with its fiduciary duties to PCSB’s stockholders under applicable law; (iii) PCSB has provided Brookline with at least three business days’ prior notice of such determination; and (iv) prior to furnishing or affording access to any information or data with respect to PCSB or any of its subsidiaries or otherwise relating to an acquisition proposal, PCSB receives from such person a confidentiality agreement with terms no less favorable to PCSB than those contained in the confidentiality agreement with Brookline, which confidentiality agreement shall not provide such person with any exclusive right to negotiate with PCSB.

PCSB’s board of directors and any committee of the board of directors will not (i) withdraw, qualify, amend or modify, or propose to withdraw, qualify, amend or modify, in a manner adverse to Brookline in connection with the transactions contemplated by the merger agreement, the recommendation of the PCSB board of directors to approve the merger agreement, fail to reaffirm the recommendation of the PCSB board of directors to approve the merger agreement within five business days following a request by Brookline, or make any statement, filing or release, in connection with the PCSB special meeting or otherwise, inconsistent with the recommendation of the PCSB board of directors to approve the merger agreement; (ii) approve or recommend, or propose to approve or recommend, any acquisition proposal; or (iii) enter into (or cause PCSB or any of its subsidiaries to enter into) any letter of intent, agreement in principle, acquisition agreement or other agreement (A) related to any acquisition transaction (other than a confidentiality agreement as described above) or (B) requiring PCSB to abandon, terminate or fail to consummate the merger or any other transaction contemplated by the merger agreement.

However, prior to the time the merger agreement is approved and adopted by the PCSB stockholders, PCSB’s board of directors may withdraw, qualify, amend or modify the recommendation of the PCSB board of directors to approve the merger agreement after the fifth business day following Brookline’s receipt of a notice from PCSB advising Brookline that PCSB’s board of directors has decided that a bona fide unsolicited written acquisition proposal that it received (and that did not result from a breach its non-solicitation obligations) constitutes a superior proposal only if (i) PCSB’s board of directors has reasonably determined in good faith, after consultation with and having considered the advice of its outside legal counsel and its financial advisor, that it is required to take such actions to comply with its fiduciary duties to PCSB’s stockholders under applicable law, (ii) during the five business day period after receipt of such notice by Brookline, PCSB and PCSB’s board of directors will cooperate and negotiate in good faith with Brookline to make such adjustments, modifications or amendments to the terms and conditions of the merger agreement as would enable PCSB to proceed with the recommendation of the PCSB board of directors to approve the merger agreement and (iii) at the end of such five business day period the PCSB board of directors again determines in good faith (A) it is required to take such actions to comply with its fiduciary duties to PCSB’s stockholders under applicable law and (B) that such acquisition proposal constitutes a superior proposal.

Conditions to the Merger (page [•])

Brookline and PCSB will not complete the merger unless a number of conditions are satisfied or waived, including:

•

the merger agreement is approved and adopted by the requisite affirmative vote of the stockholders of PCSB;

•

all regulatory approvals are obtained and remain in full force and effect and all statutory waiting periods in respect thereof having been expired, and no regulatory approval imposes any term, condition or restriction upon Brookline or any of its subsidiaries that Brookline reasonably determines is a burdensome condition;

•

the absence of any order, decree or injunction in effect, or any law, statute or regulation enacted or adopted, that enjoins, prohibits, materially restricts or makes illegal the consummation of the transactions provided for in the merger agreement;

•

the registration statement, of which this proxy statement/prospectus is a part, is declared effective and the absence of any proceeding or threatened proceeding to suspend, or stop order suspending, that effectiveness;

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•

the shares of Brookline common stock that will be issued pursuant to the merger agreement are authorized for listing on Nasdaq, subject to official notice of issuance;

•

each of the representations and warranties of the parties contained in the merger agreement are true and correct as of the date of the merger agreement and as of the closing date of the merger, unless the failure of those representations and warranties to be true and correct, individually or in the aggregate, has not had, or would not reasonably be likely to have, a material adverse effect on such party;

•

each and all of the agreements and covenants of the parties to be performed and complied with pursuant to the merger agreement on or prior to the closing date of the merger are duly performed and complied with in all material respects;

•

Brookline receives an opinion from its tax counsel, or such other counsel as provided for in the merger agreement, that the merger will be treated for federal income tax purposes as a “reorganization” under Section 368(a) of Internal Revenue Code of 1986, as amended (the “Code”); and

•

PCSB receives an opinion from its tax counsel, or such other counsel as provided for in the merger agreement, that the merger will be treated for federal income tax purposes as a “reorganization” under Section 368(a) of the Code.

Termination of the Merger Agreement (page [•])

The merger agreement may be terminated and the merger and the transactions provided for in the merger agreement abandoned as follows:

•

by mutual written consent of the parties;

•

by Brookline or PCSB if the merger is not consummated by June 1, 2023, unless the terminating party’s failure to comply with the merger agreement was the cause of the failure of the merger to occur on or before this date;

•

by Brookline or PCSB if the other party materially breaches any of its representations, warranties, covenants or agreements contained in the merger agreement (provided that the terminating party is not then in material breach of any representation, warranty, covenant or other agreement contained in the merger agreement), and the breach cannot be or has not been cured within 30 days of written notice of the breach and such breach would entitle the non-breaching party not to consummate the transactions provided for in the merger agreement;

•

by Brookline or PCSB if (1) any regulatory approval required for consummation of the merger and the other transactions provided for in the merger agreement has been denied by final nonappealable action of any regulatory authority, or (2) any governmental entity has issued a final nonappealable order, injunction or decree enjoining or otherwise prohibiting the transactions provided for in the merger agreement, provided in either case that the terminating party has used its reasonable best efforts to have the order, injunction or decree lifted;

•

by Brookline or PCSB if the required approval of the merger agreement by PCSB stockholders is not obtained;

•

by Brookline,

•

if the PCSB board of directors:

•

withdraws, qualifies, amends, modifies or withholds its recommendation to the PCSB stockholders to vote in favor of the merger or makes any statement, filing or release that is inconsistent with such recommendation;

•

materially breaches its obligation to call, give notice of, hold and commence the special meeting or to solicit proxies in favor of approval of the merger agreement and the merger;

•

in response to a tender offer or exchange offer for outstanding shares of PCSB common stock that has been publicly disclosed (other than by Brookline or an affiliate of Brookline), recommends that the holders of PCSB common stock tender their shares of PCSB

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common stock in such tender offer or exchange offer or, within ten business days after the commencement of such tender offer or exchange offer, the PCSB board of directors fails to publicly recommend against such tender offer or exchange offer within five business days of being requested to do so by Brookline (provided that Brookline may make such request only once with respect to any such tender offer or exchange offer unless such tender offer or exchange offer is subsequently modified in which case Brookline may make such request once each time such modification is made); or

•

at any time after the end of ten business days following the receipt of an acquisition proposal, fails to publicly reaffirm the recommendation to the PCSB stockholders to vote in favor of the merger within five business days following a request to do so by Brookline.

•

PCSB has breached its non-solicitation obligations.

Termination Fee (page [•])

Under the terms of the merger agreement, PCSB must pay Brookline a termination fee of $12,000,000 if:

•

Brookline terminates the merger agreement because, (i) PCSB’s board of directors (A) withdraws, qualifies, amends, modifies or withholds its recommendation, or makes any statement, filing or release, in connection with the special meeting or otherwise, inconsistent with such recommendation (it being understood that taking a neutral position or no position with respect to an acquisition proposal shall be considered an adverse modification of its recommendation), (B) materially breaches its obligation to call, give notice of and commence the special meeting under the merger agreement, (C) in response to a tender offer or exchange offer for outstanding shares of PCSB common stock that has been publicly disclosed (other than by Brookline or an affiliate of Brookline), recommends that the holders of PCSB tender their shares of PCSB common stock in such tender offer or exchange offer or, within ten business days after the commencement of such tender offer or exchange offer, the PCSB board of directors fails to publicly recommend against such tender offer or exchange offer within five business days of being requested to do so by Brookline (provided that Brookline may make such request only once with respect to any such tender offer or exchange offer unless such tender offer or exchange offer is subsequently modified in which case Brookline may make such request once each time such modification is made), or (D) at any time after the end of ten business days following the receipt of an acquisition proposal, the PCSB board of directors shall have failed to publicly reconfirm its recommendation within five business days of being requested to do so by Brookline, or (ii) there shall have been a material breach by PCSB of its non-solicitation obligations under the merger agreement;

•

Either party terminates the merger agreement because (i) the affirmative vote of holders of at least a majority of PCSB common stock outstanding and entitled to vote on the merger agreement (the “stockholder approval”) shall not have been obtained at the special meeting (provided that PCSB shall only be entitled to terminate the merger agreement if it has complied in all material respects with its obligations under the merger agreement related to the special meeting) or (ii) the merger is not consummated by June 1, 2023 (except to the extent that the failure of the merger to be consummated shall be due to the failure of the party seeking to terminate the merger agreement to perform or observe the covenants and agreements of such party set forth in the merger agreement) due to the failure to obtain the stockholder approval required for the consummation of the merger, and (A) an acquisition proposal with respect to PCSB shall have been publicly announced, disclosed or otherwise communicated to the PCSB board of directors or senior management prior to the special meeting (including any adjournment or postponement thereof) or prior to June 1, 2023, as applicable, and (B) within 12 months of such termination, PCSB will have (x) consummated a transaction qualifying as an acquisition transaction or (y) entered into a definitive agreement with respect to an acquisition transaction (however, all references in the definition of acquisition transaction to “20%” shall instead refer to “50%”); and

•

Brookline terminates the merger agreement as a result of PCSB’s intentional breach of any representation, warranty, covenant or other agreement contained in the merger agreement, which breach cannot be or has not been cured within 30 days after the giving of written notice to

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PCSB of such breach or June 1, 2023, if earlier and (i) an acquisition proposal with respect to PCSB shall have been publicly announced, disclosed or otherwise communicated to PCSB’s board of directors or senior management prior to any breach by PCSB of any representation, warranty, covenant or other agreement giving rise to such termination by Brookline or during the cure period discussed above and (ii) within 12 months of such termination, PCSB will have (A) consummated a transaction qualifying as an acquisition transaction or (B) entered into a definitive agreement with respect to an acquisition transaction (however, all references in the definition of acquisition transaction to “20%” shall instead refer to “50%”).

Effective Time of the Merger (page [•])

We expect that the merger will be completed as soon as practicable following the satisfaction or waiver of all closing conditions, including approval of the merger agreement by PCSB stockholders and receipt of all regulatory approvals. The parties cannot be certain whether or when any of the conditions to the merger will be satisfied or waived, where permissible. We currently expect to complete the merger during the second half of 2022; however, because the merger is subject to conditions beyond our control, we cannot predict the actual timing of the closing.

Material Federal Income Tax Consequences for PCSB Stockholders (page [•])

Each of Brookline and PCSB will receive an opinion of counsel to the effect that, based on certain facts, representations and assumptions, the merger will be treated as a “reorganization” pursuant to section 368(a) of the Internal Revenue Code of 1986, as amended, for federal income tax purposes. Accordingly, you generally will not recognize any gain or loss on the exchange of shares of PCSB common stock solely for shares of Brookline common stock, except with respect to any cash received in lieu of fractional shares of Brookline common stock. However, you generally will be taxed if you receive cash in exchange for your shares of PCSB common stock. Each of Brookline’s and PCSB’s obligations to complete the merger are conditioned on its receipt of this opinion, dated as of the effective date of the merger, regarding certain federal income tax consequences of the merger.

Tax matters are complicated, and the tax consequences of the merger to you will depend upon the facts of your particular situation and on whether you receive stock, cash or a mix of stock and cash in the merger. In addition, you may be subject to state, local or foreign tax laws that are not discussed in this proxy statement/​prospectus. Accordingly, we strongly urge you to consult your own tax advisor for a full understanding of the tax consequences to you of the merger.

Required Regulatory Approvals (page [•])

To complete the merger, Brookline and PCSB need the prior approval of the Board of Governors of the Federal Reserve System, or the “Federal Reserve”, the Massachusetts Commissioner of Banks (Board of Bank Incorporation), or the “BBI”, and New York State Department of Financial Services, or “NYDFS”. Prior to the PCSB special meeting, Brookline will have filed all necessary applications and notices with the applicable regulatory authorities. Brookline cannot predict, however, whether or when the required regulatory approvals will be obtained or whether any such approvals will impose any burdensome condition upon Brookline.

Accounting Treatment (page [•])

The merger will be accounted for using the acquisition method of accounting with Brookline treated as the acquiror. Under this method of accounting, PCSB’s assets and liabilities will be recorded by Brookline at their respective fair values as of the closing date of the merger. Any excess of purchase price over the net fair values of PCSB’s assets and liabilities will be recorded as goodwill. Any excess of the fair value of PCSB’s net assets over the purchase price will be recognized in earnings by Brookline on the closing date of the merger. Financial statements of Brookline issued after the merger will reflect these values, but will not be restated retroactively to reflect the historical financial position or results of operations of PCSB prior to the merger. The results of operations of PCSB will be included in the results of operations of Brookline beginning on the day after the effective date of the merger.

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Listing of Brookline Common Stock to be Issued in the Merger (page [•])

Brookline’s common stock is quoted on Nasdaq under the trading symbol “BRKL.” Under the terms of the merger agreement, Brookline will file a notice of additional listing of shares with Nasdaq with respect to the shares of Brookline common stock to be issued to the holders of PCSB common stock in the merger so that these shares will be listed and traded on Nasdaq following the merger.

Differences Between Rights of Holders of Brookline and PCSB(page [•])

The rights of PCSB stockholders currently are governed by PCSB’s charter and bylaws, and Maryland law. After the merger is completed, PCSB stockholders who receive Brookline common stock in the merger will become stockholders of Brookline, and, therefore, their rights as stockholders of Brookline will be governed by Brookline’s charter and bylaws, and by Delaware law. This means that, as a result of the merger, PCSB stockholders will have different rights when they become holders of Brookline common stock than they currently have as holders of PCSB common stock.

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RISK FACTORS

In addition to the other information contained in or incorporated by reference into this proxy statement/​prospectus, including the matters addressed in the section of this proxy statement/prospectus titled “Cautionary Statement Concerning Forward-Looking Information” on page [•], you should carefully consider the following risk factors described below in deciding how to vote. Brookline’s and PCSB’s respective businesses are subject to numerous risks and uncertainties, including the risks and uncertainties described, in the case of Brookline, in its Annual Report on Form 10-K for the year ended December 31, 2021 and in the case of PCSB, in its Annual Report on Form 10-K for the year ended June 30, 2021, each of which are incorporated by reference into this proxy statement/prospectus. See the section entitled “Where You Can Find More Information” beginning on page [•] of this proxy statement/prospectus.

Risks Relating to the Merger

Because the market price of Brookline common stock may fluctuate, you cannot be certain of the precise value of the stock portion of the merger consideration you may receive in the merger.

Upon completion of the merger, the shares of PCSB common stock outstanding immediately prior to the effective time of the merger will be converted into the right to receive consideration in the form of either cash or Brookline common stock, subject to allocation procedures to ensure that 60% of the outstanding shares of PCSB common stock will be converted to Brookline common stock. The exchange ratio for the stock portion of the merger consideration is fixed. Thus, any change in the price of Brookline common stock will affect the aggregate value of any stock consideration that PCSB stockholders receive in the merger.

There will be a time lapse between each of the date of this proxy statement/prospectus, the date on which PCSB stockholders vote to approve the merger agreement at the PCSB special meeting and the date on which PCSB stockholders entitled to receive shares of Brookline common stock actually receive such shares. The market value of Brookline common stock may fluctuate during these periods as a result of a variety of factors, including general market and economic conditions, impacts and disruptions resulting from the ongoing COVID-19 pandemic, changes in Brookline’s business, operations and prospects and regulatory considerations. Many of these factors are outside of the control of Brookline and PCSB. Consequently, at the time PCSB stockholders must decide whether to approve the merger, they will not know the actual market value of the shares of Brookline common stock they will receive when the merger is completed. The actual value of the shares of Brookline common stock received by the PCSB stockholders will depend on the market value of shares of Brookline common stock on that date. You should obtain current market quotations for shares of Brookline common stock and for shares of Brookline common stock.

PCSB stockholders may not receive the form of merger consideration that they elect.

Your right as a PCSB stockholder to receive the consideration you elect for your shares is limited because of the allocation procedures set forth in the merger agreement, which are intended to ensure that 60% of the outstanding shares of PCSB common stock will be converted to Brookline common stock. If the total stock elections by PCSB stockholders are greater, or less, than the aggregate stock consideration to be paid in the merger, you may not receive the form of consideration that you elect and you may receive a pro rata amount of cash and Brookline common stock. A detailed discussion of the election and allocation provisions of the merger agreement is set forth in the sections of this proxy statement/prospectus titled “The Merger Agreement — Merger Consideration,” “— Election Procedures” and “— Allocation Procedures,” beginning on page [•]. We recommend that you carefully read this discussion and the merger agreement attached to this proxy statement/prospectus as Annex A.

PCSB’s stockholders will have a reduced ownership and voting interest after the merger and will exercise less influence over management.

Currently, PCSB’s stockholders have the right to vote in the election of the board of directors of PCSB and the power to approve or reject any matters requiring stockholder approval under the Maryland General Corporation Law, or “MGCL”, and PCSB’s charter and bylaws. Upon the completion of the merger, each PCSB stockholder who receives shares of Brookline common stock will become a stockholder of Brookline with a percentage ownership of Brookline that is smaller than the stockholder’s current percentage

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ownership of PCSB. After the merger, former PCSB stockholders are expected to become owners of approximately [•]% of the outstanding shares of Brookline common stock, without giving effect to any shares of Brookline common stock held by PCSB stockholders prior to the merger. Even if all former PCSB stockholders voted together on all matters presented to Brookline’s stockholders, from time to time, the former PCSB stockholders would exercise significantly less influence over Brookline after the merger relative to their influence over PCSB prior to the merger, and thus would have a less significant impact on the approval or rejection of future PCSB proposals submitted to a stockholder vote.

There is no assurance when or even if the merger will be completed.

The merger agreement is subject to a number of conditions which must be fulfilled in order to complete the merger. Those conditions include:

•

approval and adoption of the merger agreement and the merger by PCSB stockholders;

•

the receipt of required regulatory approvals;

•

absence of orders prohibiting the completion of the merger;

•

effectiveness of the registration statement of which this proxy statement/prospectus is a part;

•

the continued accuracy of the representations and warranties by both parties and the performance by both parties of their covenants and agreements; and

•

the receipt by both parties of legal opinions from their respective tax counsels.

There can be no assurance that the parties will be able to satisfy the closing conditions or that closing conditions beyond their control will be satisfied or waived.

The merger agreement may be terminated in accordance with its terms and the merger may not be completed.

The merger agreement is subject to a number of conditions which must be fulfilled in order to complete the merger. Those conditions include, among other things: the approval of the proposal to approve and adopt the merger agreement by PCSB stockholders, the receipt of all required regulatory approvals, the absence of any order, injunction, or other legal restraint, the accuracy of representations and warranties under the merger agreement (subject to the materiality standards set forth in the merger agreement), Brookline’s and PCSB’s performance of their respective obligations under the merger agreement in all material respects and each of Brookline’s and PCSB’s receipt of a tax opinion to the effect that the merger will be treated as a “reorganization” within the meaning of Section 368(a) of the Code. These conditions to the closing of the merger may not be fulfilled in a timely manner or at all, and, accordingly, the merger may be delayed or may not be completed. In addition, Brookline and PCSB may opt to terminate the merger agreement under certain circumstances. Such circumstances include if the merger is not completed by June 1, 2023, either Brookline or PCSB may choose not to proceed with the merger, except to the extent that the failure to consummate the proposed merger is due to the failure of the party seeking to terminate the merger agreement to comply with its covenants and agreements. Brookline and PCSB can also mutually decide to terminate the merger agreement at any time, before or after PCSB stockholder approval. If the merger agreement is terminated under certain circumstances, PCSB may be required to pay a termination fee of $12,000,000 million to Brookline. See the section entitled “The Merger Agreement — Termination Fee” beginning on page [•] for a fuller description of these circumstances.

Regulatory approvals may not be received or may take longer than expected in order to be obtained.

Brookline is required to obtain the approvals of the Federal Reserve, the BBI, and the NYDFS prior to completing the merger. Obtaining the approval of these regulatory agencies may delay the date of completion of the merger. In addition, it is possible that, among other things, restrictions on the combined operations of the two companies may be sought by governmental agencies as a condition to obtaining the required regulatory approvals. This may diminish the benefits of the merger to Brookline or have an adverse effect on Brookline following the merger and prevent it from achieving the expected benefits of the merger. Brookline has the right to terminate the merger agreement if the approval of any governmental authority required for consummation of the merger and the other transactions provided for in the merger agreement, imposes any

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term, condition or restriction upon Brookline or any of its subsidiaries that Brookline reasonably determines would (a) prohibit or materially limit the ownership or operation by PCSB, or by Brookline or any of its subsidiaries, of all or any material portion of the business or assets of the PCSB or Brookline or any of its subsidiaries, (b) compel Brookline or any of its subsidiaries to dispose of or hold separate all or any material portion of the business or assets of PCSB or Brookline or any of its subsidiaries or (c) compel Brookline or any of its subsidiaries to take any action, or commit to take any action, or agree to any condition or request, if the prohibition, limitation, condition or other requirement described in clauses (a)-(c) of this sentence would have a material adverse effect on the future operation by Brookline and its subsidiaries of their business, taken as a whole.

PCSB’s directors and executive officers have financial interests in the merger that may be different from, or in addition to, the interests of PCSB stockholders.

Holders of PCSB common stock should be aware that some of PCSB’s directors and executive officers may have interests in the merger and have arrangements that are different from, or in addition to, those of holders of PCSB common stock generally. The PCSB board was aware of these interests and considered these interests, among other matters, when making its decision to approve the merger and merger agreement, and in recommending that stockholders vote to approve the merger agreement. See “The Merger — Interests of PCSB’s Directors and Executive Officers in the Merger” beginning on page [•].

The shares of Brookline common stock to be received by PCSB stockholders as a result of the merger will have different rights from shares of PCSB common stock.

Following completion of the proposed merger, PCSB stockholders who receive shares of Brookline common stock in the merger will become stockholders of Brookline. There will be important differences between your current rights as a PCSB stockholder and the rights to which you will be entitled as a Brookline stockholder. See the section of this proxy statement/prospectus titled “Comparison of Stockholder Rights” beginning on page [•] for a discussion of the different rights associated with Brookline common stock and PCSB common stock.

PCSB will be subject to business uncertainties and contractual restrictions while the merger is pending.

These uncertainties may impair PCSB’s ability to attract, retain and motivate key personnel until the merger is completed, and could cause customers and others who deal with PCSB and PCSB Bank to seek to change existing business relationships with PCSB and PCSB Bank. PCSB’s employee retention and recruitment may be particularly challenging prior to the effective time of the merger, as employees and prospective employees may experience uncertainty about their future roles with the combined company.

The pursuit of the merger and the preparation for the integration may place a significant burden on management and internal resources. Any significant diversion of management attention away from ongoing business and any difficulties encountered in the transition and integration process could affect PCSB’s financial results. In addition, the merger agreement requires that PCSB operate in the usual, regular and ordinary course of business and restricts PCSB from taking certain actions prior to the effective time of the merger or termination of the merger agreement without Brookline’s consent. These restrictions may prevent PCSB from pursuing attractive business opportunities that may arise prior to the completion of the merger.

If the merger is not completed, PCSB will have incurred substantial expenses without PCSB stockholders realizing the expected benefits.

PCSB has incurred, and will continue to incur, substantial expenses in connection with the transactions described in this proxy statement/prospectus. If the merger is not completed, these expenses may have a material adverse impact on the operating results of PCSB.

The opinion received by PCSB’s board of directors from Piper Sandler prior to the signing of the merger agreement will not reflect any changes in circumstances that may have occurred since the date of the opinion.

The opinion rendered by Piper Sandler, financial advisors to PCSB, to PCSB’s board of directors on May 23, 2022, to the effect that, as of such date and subject to the matters considered, assumptions made

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and qualifications and limitations as set forth therein, the merger consideration was fair, from a financial point of view, to the holders of PCSB common stock, was based upon such information available to Piper Sandler as of the date of such opinion. The opinion does not reflect any events or changes that may have occurred after the date on which such opinion was delivered, including changes to the business, financial condition, results of operations and prospects of Brookline or PCSB, changes in business, financial, economic, market and other conditions, or other events or changes which may be beyond the control of Brookline and PCSB. Any such changes may alter the relative value of Brookline or PCSB or the prices at which shares of Brookline common stock or PCSB common stock may trade prior to the time the merger is completed. The opinion does not speak as of the date the merger will be completed or as of any date other than the date of such opinion. See “The Merger — Opinion of PCSB’s Financial Advisor” and Annex B to this proxy statement/prospectus.

Litigation related to the merger may be filed against PCSB, PCSB’s board of directors, Brookline and Brookline’s board of directors in the future, which could prevent or delay the completion of the merger, result in the payment of damages or otherwise negatively impact the business and operations of Brookline and PCSB.

Litigation related to the merger may be filed against PCSB, PCSB’s board of directors, Brookline and Brookline’s board of directors in the future. The outcome of any litigation is uncertain. If any plaintiff were successful in obtaining an injunction prohibiting Brookline or PCSB from completing the merger or any of the other transactions contemplated by the merger agreement, then such injunction may delay or prevent the effectiveness of the merger and could result in significant costs to Brookline and/or PCSB, including costs in connection with the defense or settlement of any stockholder lawsuits filed in connection with the merger. Further, such lawsuits and the defense or settlement of any such lawsuits may have an adverse effect on the financial condition and results of operations of Brookline and PCSB.

Brookline may be unable to successfully integrate PCSB’s operations and may not realize the anticipated benefits of acquiring PCSB.

The merger involves the integration of two companies that previously operated independently. The difficulties of combining the companies’ operations include:

•

integrating personnel with diverse business backgrounds;

•

integrating departments, systems, operating procedures and information technologies;

•

combining different corporate cultures;

•

retaining existing customers and attracting new customers; and

•

retaining key employees.

The process of integrating operations could cause an interruption of, or loss of momentum in, the activities of one or more of the combined company’s businesses and the loss of key personnel. The diversion of management’s attention and any delays or difficulties encountered in connection with the merger and the integration of the two companies’ operations could have a material adverse effect on the business and results of operations of the combined company.

The success of the merger will depend, in part, on Brookline’s ability to realize the anticipated benefits and cost savings from combining the business of Brookline with PCSB. If Brookline is unable to successfully integrate PCSB, the anticipated benefits and cost savings of the merger may not be realized fully or may take longer to realize than expected. For example, Brookline may fail to realize the anticipated increase in earnings and cost savings anticipated to be derived from the acquisition. In addition, as with regard to any merger, a significant change in interest rates or economic conditions or decline in asset valuations may also cause Brookline not to realize expected benefits and result in the merger not being as accretive as expected.

The market price of Brookline common stock after the merger may be affected by factors different from those affecting the shares of Brookline or PCSB currently.

The businesses of Brookline and PCSB differ and, accordingly, the results of operations of the combined company and the market price of the combined company’s shares of common stock may be

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affected by factors different from those currently affecting the independent results of operations and market prices of common stock of each of Brookline and PCSB. For a discussion of the businesses of Brookline and PCSB and of certain risk factors to consider in connection with their businesses, see the documents incorporated by reference in this proxy statement/prospectus and referred to in the section of this proxy statement/prospectus titled “Where You Can Find More Information” beginning on page [•].

Risks Relating to Brookline’s Business

You should read and consider risk factors specific to Brookline’s business. These risks are described in the sections entitled “Risk Factors” in Brookline’s Annual Report on Form 10-K for the year ended December 31, 2021 and in other documents incorporated by reference into this proxy statement/prospectus. Please see the section entitled “Where You Can Find More Information” beginning on page [•] of this proxy statement/prospectus for the location of information incorporated by reference into this proxy statement/prospectus.

Risks Relating to PCSB’s Business

You should read and consider risk factors specific to PCSB’s business. These risks are described in the sections entitled “Risk Factors” in PCSB’s Annual Report on Form 10-K for the year ended June 30, 2021 and in other documents incorporated by reference into this proxy statement/prospectus. Please see the section entitled “Where You Can Find More Information” beginning on page [•] of this proxy statement/​prospectus for the location of information incorporated by reference into this proxy statement/prospectus.

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CAUTIONARY STATEMENT CONCERNING FORWARD-LOOKING INFORMATION

This proxy statement, including the information incorporated by reference, contains statements that may be considered forward-looking statements within the meaning of Section 27A of the Securities Act of 1933, as amended, and Section 21E of the Securities Exchange Act of 1934, as amended. These statements, which are based on certain current assumptions, can generally be identified by the use of the words “may,” “will,” “should,” “could,” “would,” “plan,” “potential,” “estimate,” “project,” “believe,” “intend,” “anticipate,” “expect,” “target” and similar expressions. Brookline and PCSB intend these forward-looking statements to be covered by the safe harbor provisions for forward-looking statements contained in the Private Securities Litigation Reform Act of 1995 and are including this statement for purposes of complying with these safe harbor provisions. You should read statements that contain these words carefully because they discuss the relevant company’s future expectations, contain projections of the relevant company’s future results of operations or financial condition, or state other “forward-looking” information.

The following factors, among others, could cause actual results to differ materially from the anticipated results or other expectations expressed in the forward-looking statements:

•

failure of the parties to satisfy the conditions to complete the proposed merger in a timely manner or at all;

•

failure of the stockholders of PCSB to approve and adopt the merger agreement and the merger;

•

the risk that the merger agreement may be terminated in certain circumstances;

•

failure to obtain governmental approvals or the imposition of adverse regulatory conditions in connection with such approvals;

•

the risk that any announcements relating to the proposed transaction could have adverse effects on the market price of the common stock of either or both parties to the proposed transaction;

•

the possibility that the transaction may be more expensive to complete than anticipated, including as a result of unexpected factors or events;

•

the risks relating to diversion of management’s attention from ongoing business operations and opportunities;

•

the restrictions during the pendency of the proposed merger that may impact the ability of PCSB to pursue certain business opportunities or strategic transactions;

•

disruptions to the parties’ businesses as a result of the announcement and pendency of the proposed merger;

•

difficulties in achieving cost savings as a result of the merger or in achieving such cost savings within the projected timeframe;

•

the outcome of any legal proceedings that may be instituted against PCSB, Brookline and/or others related to the merger agreement or the merger;

•

difficulties related to the integration of the businesses following the merger;

•

changes in general, national or regional economic conditions;

•

any actual or anticipated increase in inflation;

•

the impact of the ongoing COVID-19 pandemic on Brookline’s and/or PCSB’s businesses or ability to complete the proposed merger;

•

changes in loan default and charge-off rates;

•

changes in the financial performance and/or condition of borrowers;

•

changes in customer borrowing and savings habits;

•

changes in interest rates;

•

changes in regulations applicable to the financial services industry;

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•

changes in accounting or regulatory guidance applicable to banks; and

•

competition.

Additional factors that could cause Brookline’s and PCSB’s results to differ materially from those described in the forward-looking statements can be found in Brookline’s and PCSB’s filings with the SEC, including Brookline’s Annual Report on Form 10-K for the fiscal year ended December 31, 2021 and PCSB’s Annual Report on Form 10-K for the fiscal year ended June 30, 2021.

You are cautioned not to place undue reliance on the forward-looking statements, which speak only as of the date of this proxy statement/prospectus or the date of any document incorporated by reference in this proxy statement/prospectus. All subsequent written and oral forward-looking statements concerning the merger or other matters addressed in this proxy statement/prospectus and attributable to Brookline or PCSB or any person acting on their behalf are expressly qualified in their entirety by the cautionary statements contained or referred to in this section. Except to the extent required by applicable law or regulation, Brookline and PCSB undertake no obligation to update these forward-looking statements to reflect events or circumstances after the date of this proxy statement/prospectus or to reflect the occurrence of unanticipated events.

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UNAUDITED PRO FORMA CONDENSED COMBINED FINANCIAL INFORMATION

The following unaudited pro forma condensed combined financial information is based on the historical financial statements of Brookline and PCSB and has been prepared to illustrate the financial effect of the merger. The following unaudited pro forma condensed combined financial information combines the historical consolidated financial position and results of operations of Brookline and its subsidiaries and PCSB and its subsidiaries, as an acquisition by Brookline of PCSB using the acquisition method of accounting and giving effect to the related pro forma adjustments described in the accompanying notes. Under the acquisition method of accounting, the assets and liabilities of PCSB will be recorded by Brookline at their respective fair values as of the date the merger is completed.

The unaudited pro forma condensed combined balance sheet gives effect to the transaction as if the transaction had occurred on March 31, 2022. The unaudited pro forma condensed combined income statements for the three months ended March 31, 2022 and the year ended December 31, 2021 give effect to the transaction as if the transaction had become effective at January 1, 2021.

This unaudited pro forma condensed combined financial information reflects the merger of PCSB with and into Brookline based upon estimated preliminary acquisition accounting adjustments. Actual adjustments will be made as of the effective date of the merger and, therefore, may differ from those reflected in the unaudited pro forma condensed combined financial information.

Brookline and PCSB have different fiscal years. PCSB’s fiscal year ends on June 30 of each year and Brookline’s fiscal year ends on December 31 of each year. As the fiscal years differed by more than 93 days, pursuant to SEC rules, PCSB’s financial information was adjusted for the purpose of preparing the unaudited pro forma condensed statements of income. The historical income statement information of PCSB used in the unaudited pro forma condensed combined statements of income for the year ended December 31, 2021 was prepared by taking the audited condensed combined income statement for the year ended June 30, 2021, subtracting the unaudited condensed combined income statement for the six months ended December 31, 2020 and adding the unaudited condensed combined income statement for the six months ended December 31, 2021. The historical financial statement information of PCSB used in the unaudited pro forma condensed combined statements of income for the three months ended March 31, 2022 was prepared by taking the unaudited condensed combined income statement for the nine months ended March 31, 2022 and subtracting the unaudited condensed combined income statement for the six months ended December 31, 2021.

The unaudited pro forma condensed combined financial information included in this proxy statement/prospectus are presented for informational purposes only and do not necessarily reflect the financial results of the combined company had the companies actually been combined at the beginning of each period presented. The adjustments included in these unaudited pro forma condensed financial information are preliminary and may be revised. This information also does not reflect the benefits of the expected cost savings and expense efficiencies, opportunities to earn additional revenue, potential impacts of current market conditions on revenues or asset dispositions, among other factors, and includes various preliminary estimates and may not necessarily be indicative of the financial position or results of operations that would have occurred if the merger had been consummated on the date or at the beginning of the period indicated or which may be attained in the future. The unaudited pro forma combined condensed consolidated financial information has been derived from and should be read in conjunction with the historical consolidated financial statements and the related notes of Brookline, which have been separately filed by Brookline with the SEC and are incorporated by reference in this proxy statement/prospectus, and PCSB, which have been separately filed by PCSB with the SEC and are incorporated by reference in this proxy statement/prospectus.

25

BROOKLINE BANCORP INC.

CONDENSED CONSOLIDATED PRO FORMA STATEMENTS OF FINANCIAL CONDITION (Unaudited)

(in thousands)

​

At March 31, 2022

​

Brookline Historical

PCSB Historical

Adjustments (1)(2)

​

Proforma

Assets

​

​

​

​

​

​

​

​

​

​

​

​

​

Cash and short term investments

​

$

293,271

​

$

158,892

​

$

(135,011)

(3)

​

$

317,152

Securities

​

​

730,558

​

​

448,081

​

​

(47,480)

(4)

​

​

1,131,159

Loans, net of deferred fees and costs

​

​

7,223,130

​

​

1,294,597

​

​

(27,172)

(5)

​

​

8,490,555

Allowance for credit losses

​

​

(95,463)

​

​

(8,711)

​

​

(5,388)

(6)

​

​

(109,562)

Bank premises and equipment

​

​

69,365

​

​

18,904

​

​

500

(7)

​

​

88,769

Goodwill

​

​

160,427

​

​

6,106

​

​

67,513

(8)

​

​

234,046

Identifiable intangible assets

​

​

2,142

​

​

102

​

​

25,491

(9)

​

​

27,735

Other assets

​

​

250,306

​

​

66,570

​

​

13,175

(10)

​

​

330,051

Total Assets

​

$

8,633,736

​

$

1,984,541

​

$

(108,372)

​

​

$

10,509,905

Liabilities

​

​

​

​

​

​

​

​

​

​

​

​

​

Deposits

​

$

7,094,378

​

$

1,624,719

​

$

316

(11)

​

$

8,719,413

Borrowings

​

​

392,897

​

​

57,101

​

​

—

​

​

​

449,998

Other liabilities

​

​

164,526

​

​

26,329

​

​

—

​

​

​

190,855

Stockholders’ equity

​

​

981,935

​

​

276,392

​

​

(108,688)

(12)

​

​

1,149,639

Total Liabilities and Shareholders’ Equity

​

$

8,633,736

​

$

1,984,541

​

$

(108,372)

​

​

$

10,509,905

26

BROOKLINE BANCORP INC.

CONDENSED CONSOLIDATED PRO FORMA STATEMENTS OF INCOME (Unaudited)
(in thousands, except for share data)

​

Twelve Months Ended December 31, 2021

​

Brookline Historical

PCSB Historical

Adjustments (1)(2)

​

Pro Forma

INTEREST AND DIVIDEND INCOME

​

​

​

​

​

​

​

​

​

​

​

​

​

Loans and leases

​

$

297,927

​

$

49,499

​

$

5,244

(13)

​

$

352,670

Debt and equity securities

​

​

13,350

​

​

7,693

​

​

10,000

(14)

​

​

31,043

Short term investments

​

​

252

​

​

416

​

​

—

​

​

​

668

Total Interest and Dividend Income

​

​

311,529

​

​

57,608

​

​

15,244

​

​

​

384,381

INTEREST EXPENSE

​

​

​

​

​

​

​

​

​

​

​

​

​

Deposits

​

​

20,713

​

​

5,947

​

​

(105)

(15)

​

​

26,555

Borrowed Funds

​

​

8,443

​

​

1,650

​

​

—

​

​

​

10,093

Total Interest Expense

​

​

29,156

​

​

7,597

​

​

(105)

​

​

​

36,648

Net Interest Income

​

​

282,373

​

​

50,011

​

​

15,349

​

​

​

347,733

Less – (Credit) Provision for Credit Losses

​

​

(7,837)

​

​

(612)

​

​

13,145

(16)

​

​

4,696

Net Interest Income after Provision for Loan Losses

​

​

290,210

​

​

50,623

​

​

2,204

​

​

​

343,037

NONINTEREST INCOME

​

​

​

​

​

​

​

​

​

​

​

​

​

Fees and service charges

​

​

12,673

​

​

1,551

​

​

—

​

​

​

14,224

Loan level derivative income

​

​

4,680

​

​

—

​

​

—

​

​

​

4,680

Gain (Loss) on investment securities, net

​

​

(38)

​

​

113

​

​

—

​

​

​

75

Gain on sales of loans

​

​

3,737

​

​

41

​

​

—

​

​

​

3,778

Other noninterest income

​

​

5,937

​

​

1,263

​

​

—

​

​

​

7,200

Total Noninterest Income

​

​

26,989

​

​

2,968

​

​

—

​

​

​

29,957

NONINTEREST EXPENSE

​

​

​

​

​

​

​

​

​

​

​

​

​

Compensation and Employee Benefits

​

​

106,786

​

​

23,006

​

​

—

​

​

​

129,792

Occupancy, Equipment and Data Processing

​

​

33,283

​

​

7,517

​

​

—

​

​

​

40,800

Professional services

​

​

4,694

​

​

1,600

​

​

—

​

​

​

6,294

FDIC Assessment

​

​

2,980

​

​

474

​

​

—

​

​

​

3,454

Advertising and Marketing

​

​

4,167

​

​

400

​

​

—

​

​

​

4,567

Other Noninterest Expense

​

​

10,698

​

​

1,871

​

​

4,653

(17)

​

​

17,222

Total Noninterest Expense

​

​

162,608

​

​

34,868

​

​

4,653

​

​

​

202,129

Income Before Income Taxes

​

​

154,591

​

​

18,723

​

​

(2,449)

​

​

​

170,865

Provision For Income Taxes

​

​

39,151

​

​

3,819

​

​

(618)

(18)

​

​

42,352

NET INCOME

​

$

115,440

​

$

14,904

​

$

(1,831)

​

​

$

128,513

Basic Earnings Per Share

​

$

1.48

​

$

1.03

​

$

—

​

​

$

1.43

Diluted Earnings Per Share

​

$

1.48

​

$

1.03

​

$

—

​

​

$

1.43

Basic Average Shares

​

​

77,974,851

​

​

14,438,369

​

​

(2,571,387)

(19)

​

​

89,841,833

Diluted Average Shares

​

​

78,243,416

​

​

14,475,424

​

​

(2,608,442)

(19)

​

​

90,110,398

27

BROOKLINE BANCORP INC.

CONDENSED CONSOLIDATED PRO FORMA STATEMENTS OF INCOME (Unaudited)
(in thousands, except for share data)

​

Three Months Ended March 31, 2022

​

Brookline Historical

PCSB Historical

Adjustments (1)(2)

​

Pro Forma

INTEREST AND DIVIDEND INCOME

​

​

​

​

​

​

​

​

​

​

​

​

​

Loans and leases

​

$

71,721

​

$

11,943

​

$

1,311

(13)

​

$

84,975

Debt and equity securities

​

​

3,324

​

​

2,152

​

​

2,500

(14)

​

​

7,976

Short term investments

​

​

66

​

​

105

​

​

—

​

​

​

171

Total Interest and Dividend Income

​

​

75,111

​

​

14,200

​

​

3,811

​

​

​

93,122

INTEREST EXPENSE

​

​

​

​

​

​

​

​

​

​

​

​

​

Deposits

​

​

3,771

​

​

1,217

​

​

(26)

(15)

​

​

4,962

Borrowed Funds

​

​

1,492

​

​

266

​

​

—

​

​

​

1,758

Total Interest Expense

​

​

5,263

​

​

1,483

​

​

(26)

​

​

​

6,720

Net Interest Income

​

​

69,848

​

​

12,717

​

​

3,837

​

​

​

86,402

Less – (Credit) Provision for Credit Losses

​

​

(160)

​

​

286

​

​

—

(16)

​

​

126

Net Interest Income after Provision for Loan Losses

​

​

70,008

​

​

12,431

​

​

3,837

​

​

​

86,276

NONINTEREST INCOME

​

​

​

​

​

​

​

​

​

​

​

​

​

Fees and service charges

​

​

3,247

​

​

390

​

​

—

​

​

​

3,637

Loan level derivative income

​

​

686

​

​

333

​

​

—

​

​

​

1,019

Loss (Gain) on investment securities, net

​

​

—

​

​

—

​

​

—

​

​

​

—

Gain on sales of loans

​

​

344

​

​

9

​

​

—

​

​

​

353

Other noninterest income

​

​

1,252

​

​

191

​

​

—

​

​

​

1,443

Total Noninterest Income

​

​

5,529

​

​

923

​

​

—

​

​

​

6,452

NONINTEREST EXPENSE

​

​

​

​

​

​

​

​

​

​

​

​

​

Compensation and Employee Benefits

​

​

26,884

​

​

5,737

​

​

—

​

​

​

32,621

Occupancy, Equipment and Data Processing

​

​

9,362

​

​

1,987

​

​

—

​

​

​

11,349

Professional services

​

​

1,226

​

​

543

​

​

—

​

​

​

1,769

FDIC Assessment

​

​

728

​

​

125

​

​

—

​

​

​

853

Advertising and Marketing

​

​

1,272

​

​

100

​

​

—

​

​

​

1,372

Other Noninterest Expense

​

​

3,015

​

​

464

​

​

1,163

(17)

​

​

4,642

Total Noninterest Expense

​

​

42,487

​

​

8,956

​

​

1,163

​

​

​

52,606

Income Before Income Taxes

​

​

33,050

​

​

4,398

​

​

2,674

​

​

​

40,122

Provision For Income Taxes

​

​

8,345

​

​

924

​

​

675

(18)

​

​

9,944

NET INCOME

​

$

24,705

​

$

3,474

​

$

1,999

​

​

$

30,178

Basic Earnings Per Share

​

$

0.32

​

$

0.25

​

$

—

​

​

$

0.34

Diluted Earnings Per Share

​

$

0.32

​

$

0.24

​

$

—

​

​

$

0.34

Basic Average Shares

​

​

77,617,227

​

​

14,165,775

​

​

(2,298,793)

(19)

​

​

89,484,209

Diluted Average Shares

​

​

77,926,822

​

​

14,197,716

​

​

(2,330,734)

(19)

​

​

89,793,804

28

Notes to Pro Forma Combined Condensed Consolidated Financial Information (Unaudited)

1.

Estimated merger costs of $21.4 million (net of $4.2 million of taxes) are excluded from the pro forma financial information. It is expected that these costs will be recognized over time. These cost estimates for both Brookline and PCSB are forward-looking. The type and amount of actual costs incurred could vary materially from these estimates if future developments differ from the underlying assumptions used by management in determining the current estimate of these costs. The current estimates of the merger costs, primarily comprised of anticipated cash charges, are as follows:

Change in control contract and severance contracts	$	10.2
Termination of vendor and system contracts	​	2.7
Professional and legal fees	​	9.4
Other acquisition related expenses	​	3.3
Pre-tax merger costs	​	25.6
Taxes	​	4.2
Total merger costs	$	21.4

2.

Estimated expenses of approximately $10.0 million (based on the stock price of $19.11 as of March 31, 2022) associated with the termination and final allocation of PCSB’s employee stock ownership plan (“ESOP”) are excluded from the pro forma financial information. The estimated expenses will be recognized, with an equal offsetting benefit to unearned compensation and additional paid in capital within equity.

3.

Represents cash paid for 40% of outstanding common stock and all outstanding stock options.

4.

Adjustment to reflect the preliminary estimate of fair value of securities classified as held to maturity.

5.

Adjustment to reflect the preliminary estimate of fair value of acquired loans, including current interest rates and liquidity, as well as the fair value of future credit marks.

6.

Adjustments to the allowance for credit losses include the following:

Reversal of historical PCSB’s allowance for credit losses	$	8.7
Increase in allowance for credit losses for gross-up of estimated lifetime credit losses for purchased credit-deteriorated (“PCD”) loans and leases	​	(1.0)
Provision for estimate of lifetime credit losses on non-PCD loans and leases	​	(13.1)
​	$	(5.4)

7.

Adjustment to reflect bank premises and equipment values to their estimated fair value.

8.

Adjustment to eliminate historical PCSB goodwill of $6.1 million and to establish $73.6 million of goodwill for amount of consideration paid in excess of fair value of assets received over liabilities assumed.

9.

Adjustment to reflect approximately $25.6 million of core deposit intangibles at the preliminary estimated fair value and eliminate historical PCSB’s intangible assets.

10.

Adjustment to net deferred tax assets due to the business combination.

11.

Adjustment to reflect the preliminary estimate of fair value on time deposits.

12.

Adjustments to stockholders’ equity:

To eliminate PCSB’s stockholders’ equity	$	(276,392)
To reflect issuance of Brookline common stock in the merger	​	177,530
Adjustment to record provision for credit losses on non-PCD acquired loans, net of tax	​	(9,826)
​	$	(108,688)

29

13.

Adjustment reflects the yield adjustment for interest income on loans.

14

Adjustment reflects the yield adjustment for interest income on securities.

15.

Adjustment reflects the yield adjustment for interest expense on deposits.

16.

Adjustment to record provision for credit losses on non-PCD acquired loans.

17.

Adjustment reflects the net increase in amortization of other intangible assets for the acquired other intangible assets.

18.

Adjustment represents income tax expense on the pro-forma adjustments at an estimated rate of 25.25%.

19.

Adjustment to eliminate shares of PCSB common stock outstanding, reduced for shares surrendered to extinguish the outstanding ESOP loan, and to record shares of Brookline common stock outstanding using an exchange ratio of 1.3284.

Unaudited Comparative Per Share Data

The table that follows presents, for both Brookline and PCSB, historical information with respect to earnings, dividends and book value on a per share basis. The table also presents preliminary pro forma information for both companies on a per share basis.

The unaudited pro forma combined per share data set forth below gives effect to the merger as if it had occurred on January 1, 2021, the beginning of the earliest period presented, in the case of continuing net income per share data, and as of March 31, 2022, in the case of book value per share data, assuming that forty percent of the outstanding shares of PCSB common stock are exchanged for cash and the remaining shares of common stock had been converted into shares of Brookline common stock based on the exchange ratio of 1.3284 shares of Brookline common stock for each share of PCSB common stock.

The preliminary pro forma equivalent per share information shown for PCSB in the following table was obtained by multiplying the pro forma per share amounts shown for Brookline by the exchange ratio of 1.3284. The actual number of shares to be issued by Brookline in the merger will also depend on the number of shares of PCSB common stock outstanding immediately prior to the effective date of the merger.

Brookline and PCSB have different fiscal years. PCSB’s fiscal year ends on June 30 of each year and Brookline’s fiscal year ends on December 31 of each year. As the fiscal years differed by more than 93 days, pursuant to SEC rules, PCSB’s financial information was adjusted for the purpose of preparing the pro forma combined share data. The historical income statement information of PCSB used in the historical and pro forma combined share data for the year ended December 31, 2021 was prepared by taking the audited condensed combined income statement for the year ended June 30, 2021, subtracting the unaudited condensed combined income statement for the six months ended December 31, 2020 and adding the unaudited condensed combined income statement for the six months ended December 31, 2021. The historical financial statement information of PCSB used in the historical and pro forma combined share data for the three months ended March 31, 2022 was prepared by taking the unaudited condensed combined income statement for the nine months ended March 31, 2022 and subtracting the unaudited condensed combined income statement for the six months ended December 31, 2021.

The preliminary pro forma financial information includes estimated adjustments to record PCSB’s assets and liabilities at their respective fair values based on Brookline’s management’s best estimate using the information available at this time. The preliminary pro forma adjustments may be revised as additional information becomes available and as additional analyses are performed. The final allocation of the purchase price will be determined after the merger is completed and after the completion of a final analysis to determine the fair values of PCSB’s tangible and identifiable intangible assets and liabilities as of the closing date. The final purchase price adjustments may differ materially from the preliminary pro forma adjustments. Increases or decreases in the fair value of certain balance sheet amounts and other items of PCSB as compared to the information presented in this document may change the amount of the purchase price allocated to goodwill and other assets and liabilities and may impact the statement of income due to adjustments in yield and/or amortization of adjusted assets and liabilities.

30

It is anticipated that the merger will provide Brookline with financial benefits, such as possible expense efficiencies and revenue enhancements, among other factors, although no assurances can be given that these benefits will actually be achieved. The impact of these benefits has not been reflected in the preliminary pro forma financial information. As required, the preliminary pro forma financial information includes adjustments that give effect to events that are directly attributable to the merger and factually supportable. As a result, any planned adjustments affecting the balance sheet, income statement, or shares of common stock outstanding subsequent to the assumed completion date of the merger have not been included.

The preliminary pro forma financial information is presented for illustrative purposes only and is not necessarily indicative of the financial results of the combined companies had the merger actually been completed as of or at the beginning of each period presented nor does it indicate future results for any interim or full-year period.

Summary Financial Information

​	At or for the Year Ended December 31, 2021			At or for the Three Months Ended March 31, 2022
Book value per share:	​	​	​	​	​	​
Brookline historical	​	$	12.82	​	$	12.65
PCSB historical	​	​	17.92	​	​	18.02
Pro forma combined	​	​	12.98	​	​	12.85
PCSB pro forma equivalent	​	​	17.24	​	​	17.07
Tangible book value per share:	​	​	​	​	​	​
Brookline historical	​	$	10.73	​	$	10.56
PCSB historical	​	​	17.51	​	​	17.62
Pro forma combined	​	​	10.05	​	​	9.92
PCSB pro forma equivalent	​	​	13.35	​	​	13.18
Cash dividends declared per share:	​	​	​	​	​	​
Brookline historical	​	$	0.48	​	$	0.125
PCSB historical	​	​	0.22	​	$	0.060
Pro forma combined	​	​	0.48	​	$	0.125
PCSB pro forma equivalent	​	​	0.64	​	$	0.166
Basic net income per share:	​	​	​	​	​	​
Brookline historical	​	$	1.48	​	$	0.32
PCSB historical	​	​	1.03	​	​	0.25
Pro forma combined	​	​	1.43	​	​	0.34
PCSB pro forma equivalent	​	​	1.90	​	​	0.45
Diluted net income per share:	​	​	​	​	​	​
Brookline historical	​	$	1.48	​	$	0.32
PCSB historical	​	​	1.03	​	​	0.24
Pro forma combined	​	​	1.43	​	​	0.34
PCSB pro forma equivalent	​	​	1.90	​	​	0.45
Exchange ratio	​	​	1.3284	​	​	1.3284

31

THE COMPANIES

Brookline

Brookline operates as a multi-bank holding company for Brookline Bank and its subsidiaries, BankRI and its subsidiaries, Brookline Securities Corp. and Clarendon Private.

Brookline Bank, which includes its wholly owned subsidiaries, Longwood Securities Corp., First Ipswich Insurance Agency, and Eastern Funding LLC, operates 30 full-service banking offices and two lending offices in the greater Boston metropolitan area.

BankRI is headquartered in Providence, Rhode Island. BankRI, which includes its wholly owned subsidiaries, Acorn Insurance Agency, BRI Realty Corp. and BRI Investment Corp. and its wholly owned subsidiary, BRI MSC Corp., operates 20 full-service banking offices in the greater Providence, Rhode Island area.

As a commercially-focused financial institution with 50 full-service banking offices throughout greater Boston, the north shore of Massachusetts, and Rhode Island, Brookline, through Brookline Bank and BankRI, offers a wide range of commercial, business and retail banking services, including a full complement of cash management products, on-line banking services, consumer and residential loans and investment services, designed to meet the financial needs of small- to mid-sized businesses and individuals throughout central New England. Specialty lending activities including equipment financing are focused primarily in the New York and New Jersey metropolitan area. As full-service financial institutions, Brookline Bank and BankRI and their subsidiaries focus on the continued addition of well-qualified customers, the deepening of long-term banking relationships through a full complement of products and excellent customer service, and strong risk management. Clarendon Private is a registered investment advisor with the SEC. Through Clarendon Private, Brookline offers a wide range of wealth management services to individuals, families, endowments and foundations to help these clients meet their long-term financial goals.

The principal executive offices of Brookline are located at 131 Clarendon Street, Boston Massachusetts 02116, and the telephone number is (617) 425-4600.

You can find additional information about Brookline in its filings with the SEC referenced in the section in this proxy statement/prospectus titled “Where You Can Find More Information” on page [ • ].

PCSB

PCSB is the bank holding company for PCSB Bank. On April 20, 2017, PCSB completed its initial public offering in connection with PCSB Bank’s conversion from a mutual savings bank to a stock savings bank. Other than holding the common stock of PCSB Bank, PCSB has not engaged in any significant business to date.

PCSB Bank is a New York-chartered commercial bank. PCSB Bank serves the banking needs of customers in the Lower Hudson Valley of New York State through its executive offices/headquarters and 14 banking offices located in Dutchess (two offices), Putnam (three offices), Rockland (one office) and Westchester (eight offices) Counties, New York. PCSB’s primary business activity is attracting deposits from the general public and using those funds primarily to originate and purchase commercial real estate loans, business loans and one-to-four-family real estate loans and purchase investment securities.

PCSB’s primary market area encompasses all of Putnam and Westchester Counties and parts of Dutchess and Rockland Counties in New York, which are the counties in which its offices are located, and the surrounding areas.

The principal executive offices of PCSB is located at 2651 Strang Blvd., Suite 100, Yorktown Heights, New York 10598, and its telephone number is (914) 248-7272.

You can find additional information about PCSB in its filings with the SEC referenced in the section in this proxy statement/prospectus titled “Where You Can Find More Information” on page [ • ].

32

THE PCSB SPECIAL MEETING

This section contains information for PCSB stockholders about the PCSB special meeting that PCSB has called to allow PCSB stockholders to consider and vote on the PCSB merger proposal and other related matters. This proxy statement/prospectus is accompanied by a notice of the PCSB special meeting, and a form of proxy card that the PCSB board of directors is soliciting for use by PCSB stockholders at the PCSB special meeting and at any adjournments or postponements of the PCSB special meeting.

Date, Time and Place of the Meeting

The PCSB special meeting will be held on [•], 2022 at [•], local time, at PCSB’s headquarters, 2651 Strang Boulevard, Suite 100, Yorktown Heights, New York 10598.

Matters to Be Considered

At the PCSB special meeting, PCSB stockholders will be asked to consider and vote upon the following proposals:

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the PCSB merger proposal;

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the PCSB compensation proposal; and

•

the PCSB adjournment proposal.

Recommendation of PCSB’s Board of Directors

The PCSB board of directors recommends that you vote “FOR” the PCSB merger proposal, “FOR” the PCSB compensation proposal and “FOR” the PCSB adjournment proposal. See “The Merger — PCSB’s Reasons for the Merger; Recommendation of PCSB’s Board of Directors” beginning on page [•] for a more detailed discussion of the PCSB board of directors’ recommendation.

Who Can Vote and Quorum

The PCSB board of directors has fixed the close of business on [•], 2022 as the record date for determination of PCSB stockholders entitled to notice of and to vote at the PCSB special meeting. As of the record date, there were [•] shares of PCSB common stock outstanding and entitled to vote.

Holders of a majority of the outstanding shares of PCSB common stock entitled to vote at the PCSB special meeting must be present, either in attendance or by proxy, to constitute a quorum at the PCSB special meeting. If you fail to submit a proxy prior to the PCSB special meeting, or to vote at the PCSB special meeting, your shares of PCSB common stock will not be counted towards a quorum. Abstentions are considered present for the purpose of establishing a quorum but will not be counted as votes cast at the meeting.

At the PCSB special meeting, each share of PCSB common stock is entitled to one vote on all matters properly submitted to PCSB stockholders. As of the close of business on the PCSB record date, PCSB directors and executive officers and their affiliates owned and were entitled to vote approximately [ • ] shares of PCSB common stock, representing [ • ]% of the outstanding shares of PCSB common stock. Each of PCSB’s directors and executive officers has agreed to vote their shares in favor of the PCSB merger proposal, the PCSB compensation proposal and the PCSB adjournment proposal.

PCSB’s charter provides that record holders of PCSB’s common stock who beneficially own, either directly or indirectly, more than 10% of PCSB’s outstanding shares are not entitled to any vote with respect to those shares held above the 10% limit.

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Vote Required; Treatment of Abstentions and Failure to Vote

PCSB merger proposal:

•

Vote required:   Approval of the PCSB merger proposal requires the affirmative vote of a majority of the outstanding shares of PCSB common stock entitled to vote. Approval of the PCSB merger proposal is a condition to the completion of the merger.

•

Effect of abstentions and broker non-votes:   If you mark “ABSTAIN” on your proxy, fail to submit a proxy or to vote at the PCSB special meeting or fail to instruct your bank, broker, trustee or other nominee how to vote with respect to the PCSB merger proposal, it will have the same effect as a vote “AGAINST” the PCSB merger proposal.

PCSB compensation proposal:

•

Vote required:   Approval of the PCSB compensation proposal requires the affirmative vote of a majority of the votes cast by PCSB stockholders at the PCSB special meeting. Approval of the PCSB compensation proposal is not a condition to the completion of the merger.

•

Effect of abstentions and broker non-votes:   If you mark “ABSTAIN” on your proxy, fail to submit a proxy or vote at the PCSB special meeting or fail to instruct your bank, broker, trustee or other nominee how to vote with respect to the PCSB compensation proposal, you will not be deemed to have cast a vote with respect to the PCSB compensation proposal and it will have no effect on the PCSB compensation proposal.

PCSB adjournment proposal:

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Vote required:   Whether or not a quorum will be present at the meeting, approval of the PCSB adjournment proposal requires the affirmative vote of a majority of the votes cast by PCSB stockholders at the PCSB special meeting. Approval of the PCSB adjournment proposal is not a condition to the completion of the merger.

•

Effect of abstentions and broker non-votes:   If you mark “ABSTAIN” on your proxy, fail to submit a proxy or vote at the PCSB special meeting or fail to instruct your bank, broker, trustee or other nominee how to vote with respect to the PCSB adjournment proposal, you will not be deemed to have cast a vote with respect to the PCSB adjournment proposal and it will have no effect on the PCSB adjournment proposal.

Ownership of PCSB Shares, Attending the PCSB Special Meeting

You are entitled to attend the PCSB special meeting only if you were a stockholder of record at the close of business on the record date (a “record holder”) or you held your PCSB shares beneficially in the name of a bank, broker, trustee or other nominee as of the record date (a “beneficial owner”), or you hold a valid proxy for the PCSB special meeting. The PCSB special meeting will be held at our headquarters at 2651 Strang Boulevard, Suite 100, Yorktown Heights, New York on [ • ], 2022 at [ • ], local time.

You may own shares of PCSB common stock in one or more of the following ways:

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Directly in your name as the stockholder of record;

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Indirectly through a broker, bank or other holder of record in “street name”;

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Indirectly through the PCSB Bank Employee Stock Ownership Plan (the “ESOP”); or

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Indirectly through the PCSB Bank 401(k) Savings Plan (the “401(k) Plan”).

If your shares are registered directly in your name, you are the holder of record of these shares and PCSB is sending these proxy materials directly to you. As the holder of record, you have the right to give your proxy directly to us or to vote in person at the meeting.

If you hold your shares in street name, your broker, bank or other holder of record is sending these proxy materials to you. As the beneficial owner, you have the right to direct your broker, bank or other

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holder of record how to vote by filling out a voting instruction form that accompanies your proxy materials. Your broker, bank or other holder of record may allow you to provide voting instructions by telephone or by the Internet. See the instruction form provided by your broker, bank or other holder of record that accompanies this proxy statement. If you hold your shares in street name, you will need proof of ownership to be admitted to the meeting. Examples of proof of ownership are a recent brokerage statement or a letter from a bank or broker. If you want to vote your shares of PCSB common stock held in street name in person at the meeting, you must obtain a written proxy in your name from the broker, bank or other nominee who is the record holder of your shares.

If you own shares of PCSB common stock indirectly through the ESOP or the 401(k) Plan, see “— ESOP and 401(k) Plan Participant Voting” below for voting information.

ESOP and 401(k) Plan Participant Voting

If you participate in the ESOP or invest in PCSB common stock through the 401(k) Plan, you will receive a voting instruction card for each plan that reflects all shares you may direct the trustees to vote on your behalf under the plan. You may submit your voting instruction cards, or convey your voting instructions via the Internet, by telephone or by mail. Specific instructions for Internet or telephone submission are set forth on the voting instruction cards. Under the terms of the ESOP, all allocated shares of PCSB common stock held by the ESOP are voted by the ESOP trustee, as directed by plan participants. The ESOP trustee generally votes all unallocated shares of PCSB common stock held by the ESOP and allocated shares for which no timely voting instructions are received in the same proportion as shares for which the ESOP trustee has received timely voting instructions, subject to the exercise of its fiduciary duties. Under the terms of the 401(k) Plan, a participant may direct the trustee how to vote the shares of PCSB common stock credited to the Participant under the plan. PCSB will direct the 401(k) Plan trustee how to vote the shares of PCSB common stock for which timely voting instructions are not received. The deadline for returning voting instructions is [ • ], 2022.

Proxies

A holder of PCSB shares may vote by proxy or at the PCSB special meeting. If you hold your shares of PCSB common stock in your name as a record holder, to submit a proxy, you, as a holder of PCSB common stock, may use one of the following methods:

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by telephone: by calling the toll-free number indicated on the accompanying proxy card and following the recorded instructions;

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through the Internet: by visiting the website indicated on the accompanying proxy card and following the instructions; or

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by completing and returning the accompanying proxy card in the enclosed postage-paid envelope. The envelope requires no additional postage if mailed in the United States.

PCSB requests that PCSB stockholders vote by telephone, over the Internet or by completing and signing the accompanying proxy card and returning it to PCSB as soon as possible in the enclosed postage-paid envelope. When the accompanying proxy card is returned properly executed, the shares of PCSB common stock represented by it will be voted at the PCSB special meeting in accordance with the instructions contained on the proxy card. If you make no specification on your proxy card as to how you want your shares voted before signing and returning it, your proxy will be voted “FOR” the PCSB merger proposal, “FOR” the PCSB compensation proposal and “FOR” the PCSB adjournment proposal.

If you are a beneficial owner, you should check the voting form used by your bank, broker, or other holder of record to determine whether you may vote by telephone or the Internet.

Every vote is important. Accordingly, you should sign, date and return the enclosed proxy card, or vote via the Internet or by telephone, whether or not you plan to attend the PCSB special meeting. Sending in your proxy card or voting by telephone or on the Internet will not prevent you from voting your shares at the meeting.

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Voting by Proxy

PCSB is sending you this proxy statement to request that you allow your shares of PCSB common stock to be represented at the PCSB special meeting by the persons named in the enclosed proxy card. All shares of PCSB common stock represented at the meeting by properly executed and dated proxies will be voted according to the instructions indicated on the proxy card. If you sign, date and return a proxy card without giving voting instructions, your shares will be voted as recommended by the Board of Directors. The PCSB Board of Directors unanimously recommends that you vote:

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“FOR” the PCSB merger proposal;

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“FOR” the PCSB compensation proposal; and

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“FOR” the PCSB adjournment proposal.

PCSB does not currently know of any other matters to be presented at the PCSB special meeting. Execution of a proxy, however, confers discretionary authority on the designated proxy to vote the shares in accordance with their best judgment on such other business, if any, which may properly come before the PCSB special meeting or any adjournments thereof.

Instead of voting by completing and mailing a proxy card, registered stockholders can vote their shares of PCSB common stock via the Internet or by telephone. The Internet and telephone voting procedures are designed to authenticate stockholders’ identities, allow stockholders to provide their voting instructions and confirm that their instructions have been recorded properly. Specific instructions for Internet and telephone voting appear on the enclosed proxy card and for the benefit plans on the voting instruction cards. The deadline for Internet and telephone voting is [ • ], on [ • ], 2022.

Revocability of Proxies

If you directly hold shares of PCSB common stock in your name as a record holder, you can change your proxy vote at any time before your proxy is voted at the PCSB special meeting. You can do this by:

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submitting a written statement that you would like to revoke your proxy to the corporate secretary of PCSB;

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signing and returning a proxy card with a later date;

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attending the PCSB special meeting and voting at the PCSB special meeting; or

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voting by telephone or the Internet at a later time.

If you hold your shares in “street name” through a bank, broker, trustee or nominee and you have instructed the bank, broker, trustee or nominee to vote your shares, you must follow the directions received from your bank, broker, trustee or nominee to change those instructions.

Attendance at the PCSB special meeting will not in and of itself constitute revocation of a proxy. A revocation or later-dated proxy received by PCSB after the vote will not affect the vote. PCSB’s corporate secretary’s mailing address is:

PCSB Financial Corporation
2651 Strang Boulevard, Suite 100
Yorktown Heights, New York 10598
Attention: Corporate Secretary

If the PCSB special meeting is postponed or adjourned, it will not affect the ability of PCSB stockholders of record as of the record date to exercise their voting rights or to revoke any previously granted proxy using the methods described above.

Delivery of Proxy Materials

As permitted by applicable law, only one copy of this proxy statement/prospectus is being delivered to PCSB stockholders residing at the same address, unless such PCSB stockholders have notified PCSB of their desire to receive multiple copies of the proxy statement/prospectus.

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PCSB will promptly deliver, upon oral or written request, a separate copy of the proxy statement/​prospectus to any holder of PCSB common stock residing at an address to which only one copy of such document was mailed. Requests for additional copies should be directed to PCSB’s proxy solicitor, Laurel Hill Advisory Group, LLC by calling toll-free at [ • ].

Solicitation of Proxies

PCSB will pay the expenses of soliciting proxies to be voted at the PCSB special meeting. Following the original mailing of the proxies and other soliciting materials, PCSB and its officers and employees may also solicit proxies by mail, telephone, facsimile, electronic mail or in person. No additional compensation will be paid to directors, officers or other employees of PCSB for making these solicitations.

PCSB has retained a proxy solicitation firm, Laurel Hill Advisory Group, LLC, to aid it in the solicitation process. PCSB estimates it will pay Laurel Hill Advisory Group, LLC a fee of approximately $[ • ] plus certain expenses. PCSB intends to reimburse persons who hold PCSB common stock of record but not beneficially, such as brokers, custodians, nominees and fiduciaries, for their reasonable expenses in forwarding copies of proxies and other soliciting materials to, and requesting authority for the exercise of proxies from, the persons for whom they hold the shares of PCSB common stock.

You should not send in any PCSB stock certificates with your proxy card (or, if you are a beneficial owner, your voting instruction card). The exchange agent will mail a transmittal letter with instructions for the surrender of stock certificates to PCSB stockholders as soon as practicable after completion of the merger.

Other Matters to Come Before the PCSB Special Meeting

PCSB management knows of no other business to be presented at the PCSB special meeting, but if any other matters are properly presented to the meeting or any adjournments thereof, the persons named in the proxies will vote upon them in accordance with the PCSB board of directors’ recommendations.

Appraisal Rights

Under Section 3-202(c) of the MGCL, holders of PCSB common stock do not have the right to receive the appraised value of their shares in connection with the merger because those shares are listed on the Nasdaq.

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PROPOSAL NO. 1 — PCSB MERGER PROPOSAL

PCSB stockholders are being asked to approve and adopt the merger agreement and the transactions contemplated thereby, including the merger. PCSB stockholders should read this proxy statement/​prospectus carefully and in its entirety, including the annexes, for more detailed information concerning the merger agreement and the merger. A copy of the merger agreement is attached to this proxy statement/​prospectus as Annex A.

The approval of the PCSB merger proposal by PCSB stockholders is a condition to the completion of the merger. The approval of the merger agreement requires the affirmative vote of at least a majority of the outstanding shares of PCSB common stock entitled to vote thereon. Because the affirmative vote required to approve the merger agreement is based upon the total number of outstanding shares of PCSB common stock, if you fail to submit a proxy or vote at the special meeting, or vote to abstain, or you do not provide your bank, brokerage firm or other nominee with voting instructions, as applicable, this will have the same effect as a vote “AGAINST” the approval of the PCSB merger proposal.

The PCSB board, by a unanimous vote of all directors, has adopted the merger agreement and declared the merger agreement and the transactions contemplated thereby, including the merger, to be advisable and in the best interest of PCSB and PCSB stockholders. See “The Merger — PCSB’s Reasons for the Merger; Recommendation of PCSB’s Board of Directors” beginning on page [•] for a more detailed discussion of the PCSB board’s recommendation.

The PCSB board unanimously recommends a vote “FOR” the PCSB merger proposal.

THE MERGER

General

The merger agreement provides that, after approval by the stockholders of PCSB and the satisfaction or waiver of the other conditions to the merger, PCSB will merge with and into Brookline, with Brookline as the surviving company. Brookline’s charter and bylaws will be the certificate of incorporation and bylaws of the surviving company. The directors and officers of Brookline immediately prior to the merger will be the directors and officers of the surviving company. In addition, one current director of PCSB will be appointed to the board of directors of Brookline
effective as of the closing date of the merger. Following the completion of the merger, PCSB Bank will operate as a wholly owned subsidiary of Brookline and will retain its name and New York bank charter.

At the effective time of the merger, each share of PCSB common stock issued and outstanding immediately prior to the effective time of the merger will be automatically converted into the right to receive, subject to the terms and conditions of the merger agreement (including allocation procedures), at the election of the holder thereof, either: (i) $22.00 in cash or (ii) 1.3284 shares of Brookline common stock, plus cash in lieu of fractional shares. The allocation procedures included in the merger agreement are intended to ensure that 60% of the total number of shares of PCSB common stock outstanding immediately prior to the effective time of the merger will be converted into shares of Brookline common stock, and the remaining shares of PCSB common stock will be converted into cash. Shares of PCSB common stock held by Brookline or PCSB, will not be converted into the right to receive the merger consideration upon consummation of the merger.

The companies expect to complete the merger in the second half of 2022, but they must first obtain the necessary regulatory approvals and the approval of PCSB stockholders at the PCSB special meeting and satisfy other customary closing conditions. The companies cannot assure you as to when or if all the conditions to the merger will be met or waived, and it is possible they will not complete the merger at all.

Background of the Merger

Since PCSB’s initial public offering in April 2017 in connection with PCSB Bank’s conversion from the mutual form of organization to the stock form of organization, PCSB’s board of directors and senior management have periodically reviewed and assessed PCSB’s strategic alternatives and the business and

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regulatory environments facing PCSB and PCSB Bank. As part of this process, PCSB’s board of directors has periodically reviewed and discussed strategic alternatives, including a possible merger or sale transaction, and has consulted periodically with representatives of Piper Sandler regarding these matters. Piper Sandler is a nationally recognized investment banking firm with substantial experience advising financial institutions with respect to mergers and acquisitions and other matters. A predecessor to Piper Sandler, Sandler O’Neill & Partners, L.P., served as PCSB’s marketing agent in connection with its 2017 public offering. PCSB’s board of directors determined that such existing relationships would not interfere with Piper Sandler’s ability to provide financial advisory services to PCSB.

PCSB’s board of directors met on September 13, 2021, with representatives of Piper Sandler and senior management. The board of directors discussed PCSB’s historical financial performance, future prospects, and the prevailing mergers and acquisitions market, among other matters. Piper Sandler reviewed the strategic alternatives available to PCSB, including remaining independent, acquiring another financial institution, engaging in a merger-of-equals with a like-sized institution, and merging with a substantially larger institution at a premium valuation. The board of directors also discussed the perceived advantages and disadvantages of each alternative in light of the then prevailing market and economic conditions.

PCSB’s board of directors met on November 22, 2021, with representatives of Piper Sandler and senior management. The board of directors reviewed and further discussed the matters considered at the September 13, 2021 meeting. The board of directors discussed the difficulties in generating organic growth due to competition and the prevailing low market interest environment while not compromising PCSB’s strong credit culture. The board of directors also discussed the need to invest significantly in information technology and other infrastructure should PCSB continue to seek to grow organically and compete effectively, as well as the effect such investment would have on PCSB’s future earnings potential. Finally, the board of directors considered the scarcity of institutions in PCSB’s market area and surrounding area that would be suitable acquisition targets in terms of acceptable size and scale and compatible credit quality and corporate culture. At the meeting, representatives of Piper Sandler provided information regarding the then current mergers and acquisitions market, including recent bank and thrift transaction pricing. The board of directors noted that continued mergers and acquisitions activity in the bank and thrift industry would likely reduce the number of potential acquirors for PCSB. Representatives of Piper Sandler reviewed with the board of directors a discounted cash flow analysis, based on internal financial projections provided by members of PCSB’s management team, which analysis showed a range of potential values of PCSB common stock should PCSB continue to operate independently. After lengthy discussion, it was the consensus of the board of directors that Joseph D. Roberto, PCSB’s Chairman, President and Chief Executive Officer, should work with Piper Sandler to explore the levels of interest of potential acquirors of PCSB and report their findings to the board of directors.

PCSB’s board of directors met on December 22, 2021, at which meeting representatives of Piper Sandler participated. In addition to reviewing the matters discussed at the meetings held on September 13, 2021 and November 22, 2021, the board of directors reviewed and discussed a list of banking institutions, developed by Piper Sandler, which institutions Piper Sandler considered both likely to have an interest in a potential business combination with PCSB and have the capacity to pay a premium based on various assumptions and financial metrics analyzed by Piper Sandler. Included on the list was a Northeast bank holding company (Company A). On prior occasions, Company A’s Chief Executive Officer had made known to Mr. Roberto Company A’s interest in pursuing a potential business combination with PCSB. Company A demonstrated a strong capacity to pay a premium based on Piper Sandler’s analysis. After further discussion, it was the consensus of the board of directors that Mr. Roberto should meet with Company A’s Chief Executive Officer to ascertain Company A’s level of interest in pursuing a transaction.

On December 28, 2021, Mr. Roberto and Company A’s Chief Executive Officer held a virtual meeting to discuss Company A’s potential interest in a business combination with PCSB.

PCSB’s board of directors met on January 7, 2022, with representatives of Piper Sandler and representatives of PCSB’s legal counsel in attendance. Mr. Roberto reported on his meeting with Company A’s Chief Executive Officer and informed the board of directors that Company A continued to express interest in pursuing merger discussions with PCSB. The board of directors discussed PCSB’s strategic position and strategic/business plan and their previous decision to evaluate PCSB’s strategic alternatives. Representatives of Piper Sandler updated the board of directors regarding then current equity market

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conditions. After lengthy discussion and considering Company A’s capacity to pay a premium to PCSB’s stock price and other factors, the board of directors authorized Mr. Roberto to continue to engage in informal, non-binding and non-exclusive discussions with Company A regarding a potential business combination transaction.

Following the January 7th board meeting, Mr. Roberto had a telephone conversation with Company A’s Chief Executive Officer during which Company A’s Chief Executive Officer informed Mr. Roberto that Company A was not in a position to pursue merger discussions at a valuation that Company A believed PCSB would consider attractive. On January 18, 2022, Mr. Roberto met with the Chief Executive Officer of a second Northeast bank holding company (Company B) and, on January 21, 2022, Mr. Roberto met with Carl Carlson, Brookline’s Co-President and Chief Financial Officer.

PCSB’s board of directors met on January 26, 2022, with representatives of Piper Sandler and legal counsel present. Mr. Roberto informed the board of directors of Company A’s decision not to pursue merger discussions and of his informal meetings with the representatives of Company B and Brookline. He informed the board of directors that both Company B and Brookline expressed an interest in learning more about PCSB. Piper Sandler informed the board of directors that both Company B and Brookline had experience in merger and acquisition transactions and that both institutions had the capacity to provide attractive pricing terms. The board of directors reviewed an updated financial analysis prepared by Piper Sandler and discussed PCSB’s strategic position and strategic/business plan and the board’s previous decision to evaluate PCSB’s strategic alternatives. The board of directors also discussed with Piper Sandler and legal counsel the process for soliciting non-binding indications of interest from potential interested parties through the distribution of a confidential information memorandum (“CIM”). The board of directors reviewed in detail 16 identified by Piper Sandler as potentially having an interest and capacity to acquire PCSB on terms favorable to stockholders. After lengthy discussion, the board of directors authorized Piper Sandler to work with PCSB management and legal counsel to prepare a CIM and distribute it to the potential interested parties identified by Piper Sandler in consultation with PCSB, conditioned upon executing a confidentiality agreement with PCSB.

From late January through mid-February 2022, representatives of PCSB management and Piper Sandler prepared a CIM. PCSB’s legal counsel assisted PCSB in preparing a form of confidentiality agreement for use in connection with the distribution of the CIM, and PCSB populated a virtual data room containing financial and other information regarding PCSB.

From mid-February through March 2022, representatives of Piper Sandler contacted 12 potential interested parties (each of whom was on the list of potential interested parties identified by Piper Sandler) without revealing the identity of PCSB. Of the parties contacted, six signed confidentiality agreements and the identity of PCSB was disclosed to them. PCSB and Brookline entered into a confidentiality agreement on February 15, 2022. The six institutions who signed confidentiality agreements were provided with a CIM and were granted access to the virtual data room. Each confidentiality agreement included non-disclosure provisions and standstill provisions that, subject to certain exceptions, prohibits PCSB’s counterparty for 12 months from the date of such agreement, from offering to acquire or acquiring PCSB, and from taking certain other actions, including soliciting proxies, without the prior written consent of PCSB and including a provision that prohibits PCSB’s counterparty from asking PCSB to waive such standstill arrangement. As a result of this solicitation process, on March 29, 2022, Brookline, Company B and another Northeast bank holding company (Company C) submitted non-binding indication of interest letters (“IOIs”).

PCSB’s board of directors met on April 4, 2022, with representatives of Piper Sandler and legal counsel attending, to review the results of the solicitation process and the terms of the IOIs received from Brookline, Company B and Company C. Brookline’s IOI proposed a stock/cash mix of 60% stock based on a fixed exchange ratio of 1.3233 shares of Brookline common stock for each share of Company common stock and 40% cash based on a price of $21.50 per share. Company B’s IOI and Company C’s IOI also provided for a stock/cash mix, but both provided lower nominal pricing terms than Brookline. Unlike Company B’s and Company C’s IOIs, which provided for merging PCSB Bank into Company B’s and Company’s C’s respective bank subsidiaries, Brookline’s IOI provided for operating PCSB Bank as a separate subsidiary alongside Brookline’s two existing bank subsidiaries. All three IOIs requested a period of exclusivity to negotiate with PCSB. As part of this discussion, Piper Sandler updated the board of directors regarding the then current bank and thrift mergers and acquisitions market. The board of directors also

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reviewed again its decision to seek a strategic partner and noted the significant increases in business uncertainties since the beginning of 2022, including rising market interest rates, growing inflation expectations, and declining stock prices, as well as the potential impact of such conditions on PCSB. After lengthy discussion, the board of directors authorized Piper Sandler to contact Brookline, Company B and Company C and request that they improve the financial terms of their IOIs in exchange for an exclusivity agreement with PCSB.

On April 7, 2022, Company C submitted a revised IOI, which provided lower nominal pricing terms than Brookline’s revised IOI.

On April 8, 2022, Brookline submitted a revised IOI, which increased the stock exchange ratio from 1.3233 to 1.3284 and the cash consideration from $21.50 per share to $21.60 per share and revised the stock/​cash mix from 60%/40% to 65%/35%.

PCSB’s board of directors met on April 11, 2022, with representatives of Piper Sandler and legal counsel attending, to review the revised IOIs received from Brookline and Company C. Company B reiterated the terms of its original IOI. Following a lengthy discussion of the revised IOIs, the board of directors authorized Piper Sandler to contact Brookline, Company B and Company C and again request that they improve the financial terms of their IOIs in exchange for an exclusivity agreement with PCSB.

On April 12, 2022, Brookline submitted a revised IOI that reflected an increase in the cash merger consideration from $21.60 per share to $22.00 per share and reverted to the original stock/cash mix of 60%/40%. The stock exchange ratio was unchanged at 1.3284.

PCSB’s board of directors met on April 13, 2022, with representatives of Piper Sandler and legal counsel attending, to review the revised IOI submitted by Brookline on April 12, 2022. Based on the board of directors’ review of the revised IOIs and of certain financial analysis prepared by Piper Sandler and summarized by Piper Sandler at the meeting, the board of directors determined that the nominal value of the Brookline proposal was significantly higher than the proposals of Company B and Company C. Following a lengthy discussion of Brookline’s revised IOI and other matters, including a discussion of the recent decline in stock prices of publicly-traded financial institutions, the board of directors approved the terms of the revised IOI and authorized entering into an exclusivity agreement with Brookline.

On April 18, 2022, PCSB and Brookline entered into an exclusivity agreement providing for a period of exclusive negotiations up to May 31, 2022.

Over the following weeks, Brookline conducted due diligence on PCSB and PCSB conducted reverse due diligence on Brookline.

On May 2, 2022, Brookline’s legal counsel distributed an initial draft of the merger agreement to Luse Gorman. Between May 9, 2022 and May 22, 2022, multiple drafts of the merger agreement were exchanged, and representatives of Brookline’s legal counsel and representatives of PCSB’s legal counsel participated in calls to discuss open issues, which included deal protections, termination fees, the conduct of PCSB’s business prior to closing, certain representations and warranties and employee matters.

PCSB’s board of directors met on May 18, 2022, with representatives of Piper Sandler and legal counsel in attendance, to discuss the then current status of the merger agreement negotiations. Management reported that the reverse due diligence conducted on Brookline generally confirmed its expectations as to Brookline. Piper Sandler summarized the solicitation process and provided preliminary financial information regarding the merger consideration. Legal counsel reviewed the most recent draft of the merger agreement and, together with management, updated the board of directors on terms that were still under negotiation.

PCSB’s board of directors met on May 23, 2022, with representatives of Piper Sandler and legal counsel in attendance, to consider the approval of the merger agreement and the transactions contemplated by it. Before the meeting, management distributed to each director the proposed merger agreement and a financial presentation prepared by Piper Sandler. Piper Sandler reviewed in detail the pricing and other financial terms of the proposed merger agreement. Legal counsel reviewed in detail the terms and conditions of the proposed merger agreement, including, but not limited to, the transaction structure, the representations, warranties and covenants made by PCSB and Brookline, the closing conditions, and the termination

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rights of PCSB and Brookline. The board of directors reviewed all aspects of the merger process, including PCSB’s current financial position, performance and prospects, including the impact of rising interest rates, its decision to pursue a strategic transaction, the process that was used to identify potential merger partners and solicit merger proposals, then current economic and stock market conditions, PCSB’s due diligence investigation of Brookline, the terms and conditions of the proposed merger agreement, the value of the proposed merger consideration, and the impact of the proposed merger on PCSB’s stockholders and other constituencies. All questions posed by the directors were answered by management, representatives of Piper Sandler or legal counsel, as appropriate. Piper Sandler then rendered its oral opinion to the board of directors, which was subsequently confirmed in writing, to the effect that, as of May 23, 2022, and subject to the procedures followed, assumptions made, matters considered, and qualifications and limitations on the review undertaken by Piper Sandler as set forth in such opinion, the merger consideration to be paid by Brookline to PCSB’s common stockholders pursuant to the proposed merger agreement was fair to PCSB’s common stockholders from a financial point of view. After considering the proposed merger agreement, and ancillary documents, and taking into consideration the matters discussed at the meeting and at prior meetings of the board of directors, the board of directors voted unanimously to adopt and approve the proposed merger agreement, to recommend that PCSB’s stockholders vote to approve the proposed merger agreement, and to authorize Mr. Roberto to execute and deliver the merger agreement, and all ancillary documents, on behalf of PCSB.

On May 23, 2022, PCSB and Brookline executed the merger agreement and, on May 24, 2022, before the opening of the stock markets, issued a joint press release to announce publicly the execution of the merger agreement.

Reasons for the Merger

PCSB’s board of directors reviewed and discussed the merger agreement, and the transactions contemplated by it, together with PCSB management and PCSB’s financial and legal advisors, in determining that the merger agreement and the transactions contemplated by it are advisable and in the best interests of PCSB and its stockholders. In reaching its conclusion to approve the merger agreement and the transactions contemplated by it, the board of directors considered a number of factors. The material factors considered by the board of directors were as follows:

•

Its understanding of the business, operations, financial condition, earnings, and future prospects of PCSB;

•

Its recognition that PCSB’s ability to grow organically would require substantial investment in information technology and other infrastructure, and the effect such investment would have on PCSB’s future earnings potential;

•

Its recognition that PCSB’s ability to grow through acquisitions was limited based on the scarcity of acquisition candidates in PCSB’s geographic market area and surrounding areas that PCSB considered attractive;

•

National and local economic conditions, particularly the uncertainty as to future economic conditions given the recent rise in market interest rates, expected future increases in market interest rates, growing inflation expectations, and other factors, and the expected effect of these conditions on PCSB’s financial condition, earnings, and prospects, as well as the stock prices of financial institutions, including PCSB;

•

The value of the merger consideration proposed by Brookline compared to the value of the merger consideration proposed by other parties and the estimated potential future value of PCSB’s common stock if PCSB would continue to operate on a stand-alone basis;

•

The competitive environment for financial institutions generally and in PCSB’s geographic market area in particular, and the trend toward consolidation in the financial services industry;

•

Brookline’s ability to pay the merger consideration and obtain regulatory approval for the merger, considering PCSB’s due diligence investigation of Brookline;

•

The scope and results of the solicitation process conducted by PCSB, with the assistance of Piper Sandler;

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•

The complementary business cultures of PCSB and Brookline;

•

The historical market prices and the then current market price for PCSB’s common stock;

•

The cash merger consideration component, although taxable to a PCSB stockholder, offered value certainty to counteract potential decreases in Brookline’s stock price;

•

The review by the board of directors, with the assistance of legal counsel, of the terms of the merger agreement, including the provisions of the merger agreement that permit PCSB, under certain circumstances, to furnish information to and conduct negotiations with third parties regarding a business combination transaction, subject, in certain circumstances, to paying Brookline a $12.0 million cash termination fee;

•

The perceived favorable impact of the merger on the employees, depositors, customers, and communities served by PCSB Bank, considering that PCSB Bank would operate as a separate subsidiary of Brookline and Brookline would select a member of PCSB’s board of directors to serve as a director of Brookline; and

•

The opinion of Piper Sandler, dated May 23, 2022, addressed to PCSB’s board of directors, as to the fairness of the merger consideration to PCSB’s common stockholders from a financial point of view, as more fully described under “Opinion of PCSB’s Financial Advisor.”

PCSB’s board of directors also considered potential risks associated with the transactions contemplated by the merger agreement, including:

•

The interests of PCSB’s executive officers and directors with respect to the transactions contemplated by the merger agreement apart from their interests as stockholders of PCSB as disclosed under “Interests of PCSB’s Directors and Executive Officers in the Merger,” and the risk that these interests might influence their decision with respect to the merger agreement;

•

The risk that the merger agreement provisions relating to the payment of a termination fee under specified circumstances, although required by Brookline as a condition to entering into the merger agreement, could discourage other parties that may be interested in engaging in a business combination transaction with PCSB from proposing it;

•

The risk of litigation;

•

The restrictions imposed by the merger agreement on the conduct of PCSB’s business before completion of the merger which could delay or prevent PCSB from undertaking some business opportunities that may arise during that time;

•

That the fixed exchange ratio for the stock consideration, by its nature, would not adjust upward to compensate for any declines in Brookline’s stock price before the completion of the merger, meaning that PCSB’s stockholders would not be protected against any decrease in Brookline’s stock price before the completion of the merger; and

•

The need to obtain approval from PCSB’s stockholders and governmental approvals in order to consummate the merger.

PCSB’s board of directors evaluated the factors described above and reached consensus that the merger agreement and the merger contemplated by it were in the best interests of PCSB and its stockholders. Accordingly, the board of directors unanimously approved the merger agreement and unanimously recommends that PCSB’s stockholders vote “FOR” approval of the merger agreement and transactions contemplated by it.

The foregoing discussion of the information and factors considered by PCSB’s board of directors is not intended to be exhaustive but constitutes the material factors considered by the board of directors. In reaching its determination to approve the merger agreement and recommend that PCSB’s stockholders vote to approve the merger agreement, PCSB’s board of directors did not assign any relative or specific weights to the foregoing factors, and individual directors may have weighed factors differently. The terms of the merger agreement were the product of arm’s length negotiations between representatives of PCSB and Brookline.

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Recommendation of the PCSB Board of Directors

The PCSB board of directors unanimously approved the merger agreement and unanimously recommends that PCSB’s stockholders vote “FOR” approval of the merger agreement and transactions contemplated by it.

Opinion of PCSB’s Financial Advisor

Pursuant to an engagement letter dated February 11, 2022, PCSB retained Piper Sandler to act as financial advisor to PCSB’s board of directors in connection with PCSB’s consideration of a possible business combination. PCSB selected Piper Sandler to act as its financial advisor because Piper Sandler is a nationally recognized investment banking firm whose principal business specialty is financial institutions. In the ordinary course of its investment banking business, Piper Sandler is regularly engaged in the valuation of financial institutions and their securities in connection with mergers and acquisitions and other corporate transactions.

Piper Sandler acted as financial advisor to PCSB’s board of directors in connection with the proposed merger and participated in certain of the negotiations leading to the execution of the merger agreement. At the May 23, 2022 meeting at which PCSB’s board of directors considered the merger and the merger agreement, Piper Sandler delivered to the board of directors its oral opinion, which was subsequently confirmed in writing on May 23, 2022, to the effect that, as of such date, the merger consideration was fair to the holders of PCSB’s common stock from a financial point of view. The full text of Piper Sandler’s opinion is attached as Annex [B] to this proxy statement/prospectus. The opinion outlines the procedures followed, assumptions made, matters considered and qualifications and limitations on the review undertaken by Piper Sandler in rendering its opinion. The description of the opinion set forth below is qualified in its entirety by reference to the full text of the opinion. Holders of PCSB common stock are urged to read the entire opinion carefully in connection with their consideration of the proposed merger.

Piper Sandler’s opinion was directed to the board of directors of PCSB in connection with its consideration of the merger and the merger agreement and does not constitute a recommendation to any stockholder of PCSB as to how any such stockholder should vote at any meeting of stockholders called to consider and vote upon the approval of the merger and the merger agreement. Piper Sandler’s opinion was directed only to the fairness, from a financial point of view, of the merger consideration to the holders of PCSB common stock and did not address the underlying business decision of PCSB to engage in the proposed merger, the form or structure of the proposed merger or any other transactions contemplated in the merger agreement, the relative merits of the proposed merger as compared to any other alternative transactions or business strategies that might exist for PCSB or the effect of any other transaction in which PCSB might engage. Piper Sandler also did not express any opinion as to the fairness of the amount or nature of the compensation to be received in the proposed merger by any officer, director or employee of PCSB, or any class of such persons, if any, relative to the compensation to be received in the proposed merger by any other stockholder. Piper Sandler’s opinion was approved by Piper Sandler’s fairness opinion committee.

In connection with its opinion, Piper Sandler reviewed and considered, among other things:

•

a draft of the merger agreement, dated May 23, 2022;

•

certain publicly available financial statements and other historical financial information of PCSB and its banking subsidiary, PCSB Bank, that Piper Sandler deemed relevant;

•

certain publicly available financial statements and other historical financial information of Brookline and its banking subsidiaries, Brookline Bank and Bank Rhode Island, that Piper Sandler deemed relevant;

•

certain internal financial projections for PCSB for the years ending June 30, 2022 through June 30, 2026, as provided by the senior management of PCSB;

•

balance sheet and earnings per share estimates for Brookline for the years ending December 31, 2022 through December 31, 2023 based on publicly available mean analyst estimates for Brookline, as well as an estimated long-term annual earnings per share growth rate for the years ending December 31,

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2024 through December 31, 2026 and estimated dividends per share for Brookline for the years ending December 31, 2022 through December 31, 2026, as provided by the senior management of Brookline;

•

the pro forma financial impact of the proposed merger on Brookline based on certain assumptions relating to transaction expenses, cost savings and purchase accounting adjustments, as provided by the senior management of Brookline, as well as estimated net income for PCSB for the years ending December 31, 2022 through December 31, 2026, as provided by the senior management of PCSB and adjusted by the senior management of Brookline;

•

the publicly reported historical price and trading activity for PCSB common stock and Brookline common stock, including a comparison of certain stock trading information for PCSB common stock and Brookline common stock and certain stock indices as well as similar publicly available information for certain other companies, the securities of which are publicly traded;

•

a comparison of certain financial and market information for PCSB and Brookline with similar financial institutions for which information is publicly available;

•

the financial terms of certain recent business combinations in the bank and thrift industry (on a regional and nationwide basis), to the extent publicly available;

•

the current market environment generally and the banking environment in particular; and

•

such other information, financial studies, analyses and investigations and financial, economic and market criteria as Piper Sandler considered relevant.

Piper Sandler also discussed with certain members of the senior management of PCSB and its representatives the business, financial condition, results of operations and prospects of PCSB and held similar discussions with certain members of the senior management of Brookline and its representatives regarding the business, financial condition, results of operations and prospects of Brookline.

In performing its review, Piper Sandler relied upon the accuracy and completeness of all of the financial and other information that was available to and reviewed by Piper Sandler from public sources, that was provided to Piper Sandler by PCSB or Brookline or their respective representatives, or that was otherwise reviewed by Piper Sandler, and Piper Sandler assumed such accuracy and completeness for purposes of rendering its opinion without any independent verification or investigation. Piper Sandler relied on the assurances of the respective managements of PCSB and Brookline that they were not aware of any facts or circumstances that would have made any of such information inaccurate or misleading. Piper Sandler was not asked to and did not undertake an independent verification of any of such information and Piper Sandler did not assume any responsibility or liability for the accuracy or completeness thereof. Piper Sandler did not make an independent evaluation or perform an appraisal of the specific assets, the collateral securing assets or the liabilities (contingent or otherwise) of PCSB or Brookline, nor was Piper Sandler furnished with any such evaluations or appraisals. Piper Sandler rendered no opinion or evaluation on the collectability of any assets or the future performance of any loans of PCSB or Brookline. Piper Sandler did not make an independent evaluation of the adequacy of the allowance for loan losses of PCSB or Brookline, or of the combined entity after the proposed merger, and Piper Sandler did not review any individual credit files relating to PCSB or Brookline. Piper Sandler assumed, with PCSB’s consent, that the respective allowances for loan losses for both PCSB and Brookline were adequate to cover such losses and would be adequate on a pro forma basis for the combined entity.

In preparing its analyses, Piper Sandler used certain internal financial projections for PCSB for the years ending June 30, 2022 through June 30, 2026, as provided by the senior management of PCSB. In addition, Piper Sandler used balance sheet and earnings per share estimates for Brookline for the years ending December 31, 2022 and December 31, 2023 based on publicly available mean analyst estimates for Brookline, as well as an estimated long-term annual earnings per share growth rate for the years ending December 31, 2024 through December 31, 2026 and estimated dividends per share for Brookline for the years ending December 31, 2022 through December 31, 2026, as provided by the senior management of Brookline. Piper Sandler also received and used in its pro forma analyses certain assumptions relating to transaction expenses, cost savings and purchase accounting adjustments, as provided by the senior management of Brookline, as well as estimated net income for PCSB for the years ending December 31, 2022 through

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December 31, 2026, as provided by the senior management of PCSB and adjusted by the senior management of Brookline. With respect to the foregoing information, the respective senior managements of PCSB and Brookline confirmed to Piper Sandler that such information reflected (or, in the case of the publicly available analyst estimates referred to above, were consistent with) the best currently available projections, estimates and judgments of those respective senior managements as to the future financial performance of PCSB and Brookline, respectively, and the other matters covered thereby, and Piper Sandler assumed that the future financial performance reflected in such information would be achieved. Piper Sandler expressed no opinion as to such information, or the assumptions on which such information was based. Piper Sandler also assumed that there had been no material change in the respective assets, financial condition, results of operations, business or prospects of PCSB or Brookline since the date of the most recent financial statements made available to Piper Sandler. Piper Sandler assumed in all respects material to its analyses that PCSB and Brookline would remain as going concerns for all periods relevant to its analyses.

Piper Sandler also assumed, with PCSB’s consent, that (i) each of the parties to the merger agreement would comply in all material respects with all material terms and conditions of the merger agreement and all related agreements, that all of the representations and warranties contained in such agreements were true and correct in all material respects, that each of the parties to such agreements would perform in all material respects all of the covenants and other obligations required to be performed by such party under such agreements and that the conditions precedent in such agreements were not and would not be waived, (ii) in the course of obtaining the necessary regulatory or third party approvals, consents and releases with respect to the merger, no delay, limitation, restriction or condition would be imposed that would have an adverse effect on PCSB, Brookline, the merger or any related transactions, and (iii) the merger and any related transactions would be consummated in accordance with the terms of the merger agreement without any waiver, modification or amendment of any material term, condition or agreement thereof and in compliance with all applicable laws and other requirements. Finally, with PCSB’s consent, Piper Sandler relied upon the advice that PCSB received from its legal, accounting and tax advisors as to all legal, accounting and tax matters relating to the merger and the other transactions contemplated by the merger agreement. Piper Sandler expressed no opinion as to any such matters.

Piper Sandler’s opinion was necessarily based on financial, regulatory, economic, market and other conditions as in effect on, and the information made available to Piper Sandler as of, the date thereof. Events occurring after the date thereof could materially affect Piper Sandler’s opinion. Piper Sandler has not undertaken to update, revise, reaffirm or withdraw its opinion or otherwise comment upon events occurring after the date thereof. Piper Sandler expressed no opinion as to the trading value of PCSB common stock or Brookline common stock at any time or what the value of Brookline common stock would be once it is actually received by the holders of PCSB common stock.

In rendering its opinion, Piper Sandler performed a variety of financial analyses. The summary below is not a complete description of all the analyses underlying Piper Sandler’s opinion or the presentation made by Piper Sandler to PCSB’s board of directors, but is a summary of the material analyses performed and presented by Piper Sandler. The summary includes information presented in tabular format. In order to fully understand the financial analyses, these tables must be read together with the accompanying text. The tables alone do not constitute a complete description of the financial analyses. The preparation of a fairness opinion is a complex process involving subjective judgments as to the most appropriate and relevant methods of financial analysis and the application of those methods to the particular circumstances. The process, therefore, is not necessarily susceptible to a partial analysis or summary description. Piper Sandler believes that its analyses must be considered as a whole and that selecting portions of the factors and analyses to be considered without considering all factors and analyses, or attempting to ascribe relative weights to some or all such factors and analyses, could create an incomplete view of the evaluation process underlying its opinion. Also, no company included in Piper Sandler’s comparative analyses described below is identical to PCSB or Brookline and no transaction is identical to the proposed merger. Accordingly, an analysis of comparable companies or transactions involves complex considerations and judgments concerning differences in financial and operating characteristics of the companies and other factors that could affect the public trading values or transaction values, as the case may be, of PCSB and Brookline and the companies to which they were compared. In arriving at its opinion, Piper Sandler did not attribute any particular weight to any analysis or factor that it considered. Rather, Piper Sandler made qualitative judgments as to the significance and relevance of each analysis and factor. Piper Sandler did not form an opinion as to whether any individual

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analysis or factor (positive or negative) considered in isolation supported or failed to support its opinion, rather, Piper Sandler made its determination as to the fairness of the merger consideration to the holders of PCSB common stock on the basis of its experience and professional judgment after considering the results of all its analyses taken as a whole.

In performing its analyses, Piper Sandler also made numerous assumptions with respect to industry performance, business and economic conditions and various other matters, many of which cannot be predicted and are beyond the control of PCSB, Brookline and Piper Sandler. The analyses performed by Piper Sandler are not necessarily indicative of actual values or future results, both of which may be significantly more or less favorable than suggested by such analyses. Piper Sandler prepared its analyses solely for purposes of rendering its opinion and provided such analyses to PCSB’s board of directors at its May 23, 2022 meeting. Estimates on the values of companies do not purport to be appraisals or necessarily reflect the prices at which companies or their securities may actually be sold. Such estimates are inherently subject to uncertainty and actual values may be materially different. Accordingly, Piper Sandler’s analyses do not necessarily reflect the value of PCSB common stock or Brookline common stock or the prices at which PCSB or Brookline common stock may be sold at any time. The analyses of Piper Sandler and its opinion were among a number of factors taken into consideration by PCSB’s board of directors in making its determination to approve the merger and the analyses described below should not be viewed as determinative of the decision of PCSB’s board of directors with respect to the fairness of the merger consideration.

Summary of Proposed Merger Consideration and Implied Transaction Metrics.

Piper Sandler reviewed the financial terms of the proposed merger. Pursuant to the terms of the merger agreement, at the effective time of the merger, each share of PCSB common stock issued and outstanding immediately prior to the effective time of the transaction, except for certain shares as set forth in the merger agreement, shall be converted into, as provided in and subject to the limitations set forth in the merger agreement, the right to receive, at the election of the holder thereof, either (i) $22.00 in cash, without interest, or (ii) 1.3284 shares of Brookline common stock. The merger agreement provides, generally, that 60 percent (60%) of the shares of PCSB common stock issued and outstanding immediately prior to the effective time of the transaction shall be converted into Brookline common stock and each of the remaining shares of PCSB common stock shall be converted into $22.00 in cash. Piper Sandler calculated an aggregate implied transaction value of approximately $319.0 million and an implied purchase price per share of $20.54 consisting of the implied value of 15,334,857 shares of PCSB common stock and 1,320,963 PCSB stock options with a weighted average strike price of $18.98 based on the closing price of Brookline common stock on May 20, 2022 (the last trading day before the public announcement of the proposed merger). Based upon financial information for PCSB as of or for the last twelve months (“LTM”) ended March 31, 2022 and the closing price of PCSB’s common stock on May 20, 2022, Piper Sandler calculated the following implied transaction metrics:

Transaction Price / LTM Earnings	21.6x
Transaction Price / Estimated FY 2022 Earnings(1)	20.8x
Transaction Price / Estimated FY 2023 Earnings(1)	19.6x
Transaction Price / Tangible Book Value	118.1%
Transaction Price / Adjusted Tangible Book Value(2)	127.2%
Core Deposit Premium(3)	3.1%
Market Premium as of May 20, 2022	13.2%

(1)

Based on PCSB internal financial projections

(2)

Tangible book value adjusted to a TCE / TA ratio of 9.50%; assumes a dollar-for-dollar payout on capital in excess of 9.50% TCE / TA

(3)

Core deposits defined as total deposits less time deposits > $250,000

Note: Transaction values and implied multiples presented gross of the extinguishment of PCSB’s ESOP loan assuming the balance at March 31, 2022 of $9.7 million

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Stock Trading History.

Piper Sandler reviewed the publicly available historical reported trading prices of PCSB common stock and Brookline common stock for the one-year and three-year periods ended May 20, 2022. Piper Sandler then compared the relationship between the movements in the price of PCSB common stock and Brookline common stock, respectively, to movements in their respective peer groups (as described below) as well as certain stock indices.

PCSB’s One-Year Stock Performance

​	Beginning Value May 20, 2021		Ending Value May 20, 2022
PCSB	​	100%	​	100.2%
PCSB Peer Group	​	100%	​	99.5%
S&P 500 Index	​	100%	​	93.8%
Nasdaq Bank Index	​	100%	​	86.6%

PCSB’s Three-Year Stock Performance

​	Beginning Value May 20, 2019		Ending Value May 20, 2022
PCSB	​	100%	​	94.3%
PCSB Peer Group	​	100%	​	125.7%
S&P 500 Index	​	100%	​	137.4%
Nasdaq Bank Index	​	100%	​	112.4%

Brookline’s One-Year Stock Performance

​	Beginning Value May 20, 2021		Ending Value May 20, 2022
Brookline	​	100%	​	87.7%
Brookline Peer Group	​	100%	​	88.1%
S&P 500 Index	​	100%	​	93.8%
Nasdaq Bank Index	​	100%	​	86.6%

Brookline’s Three-Year Stock Performance

​	Beginning Value May 20, 2019		Ending Value May 20, 2022
Brookline	​	100%	​	97.2%
Brookline Peer Group	​	100%	​	93.8%
S&P 500 Index	​	100%	​	137.4%
Nasdaq Bank Index	​	100%	​	112.4%

Comparable Company Analyses.

Piper Sandler used publicly available information to compare selected financial information for PCSB with a group of financial institutions selected by Piper Sandler based on its experience and professional judgment. The PCSB peer group included nationwide thrifts converted after January 1, 2013 whose securities are traded on a major exchange with total assets between $500 million and $6 billion, excluding targets of announced merger transactions (the “PCSB Peer Group”). The PCSB Peer Group consisted of the following companies:

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1895 Bancorp of Wisconsin,
Affinity Bancshares, Inc.
Blue Foundry Bancorp
First Northwest Bancorp
Five Star Bancorp
HarborOne Bancorp, Inc.
HV Bancorp, Inc.
Magyar Bancorp, Inc. Northeast Community Bancorp, Inc.
Northfield Bancorp, Inc.
Pathfinder Bancorp, Inc.
Ponce Financial Group, Inc.
Provident Bancorp, Inc.
Richmond Mutual Bancorporation, Inc.
Waterstone Financial, Inc.
William Penn Bancorporation

The analysis compared financial information for PCSB with corresponding data for the PCSB Peer Group as of or for the year ended March 31, 2022 (unless otherwise noted) with pricing data as of May 20, 2022. The table below sets forth the data for PCSB and the median, mean, low and high data for the PCSB Peer Group.

PCSB Comparable Company Analysis

​	PCSB		PCSB Peer Group Median		PCSB Peer Group Mean		PCSB Peer Group Low		PCSB Peer Group High
Market Capitalization ($mm)	​	278	​	170	​	246	​	43	​	655
Price / Tangible Book Value (%)	​	103	​	96	​	101	​	70	​	188
Price / LTM Earnings Per Share (x)	​	17.8	​	13.2	​	14.1	​	7.1	​	42.7
Price / 2022E Earnings Per Share (x)	​	17.8	​	11.5	​	17.0	​	9.3	​	53.8
Price / 2023E Earnings Per Share (x)	​	17.4	​	10.4	​	15.5	​	7.5	​	38.7
Current Dividend Yield (%)	​	1.5	​	2.1	​	2.3	​	1.0	​	4.9
Total Assets ($mm)	​	1,985	​	1,462	​	1,848	​	546	​	5,516
Loans / Deposits (%)	​	79.7	​	93.1	​	91.4	​	70.0	​	111.5
Non-performing Assets(1) / Total Assets (%)	​	0.44	​	0.63	​	0.70	​	0.05	​	1.47
Loan Loss Reserve / Gross Loans (%)	​	0.67	​	1.13	​	1.12	​	0.53	​	1.52
Net Charge-offs / Average Loans (%)	​	0.00	​	0.01	​	0.03	​	(0.18)	​	0.30
Tangible Common Equity / Tangible Assets (%)	​	13.66	​	12.96	​	14.29	​	7.44	​	23.24
Total Risk-based Capital Ratio (%)	​	—	​	15.28	​	17.57	​	13.07	​	28.96
Most Recent Quarter (MRQ) Return on Average Assets (%)	​	0.73	​	0.96	​	0.87	​	NM	​	1.51
MRQ Return on Average Tangible Common Equity (%)	​	5.15	​	6.97	​	6.93	​	NM	​	16.83
MRQ Net Interest Margin (%)	​	2.80	​	3.22	​	3.37	​	2.36	​