SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

SCHEDULE 13D

(Amendment No.     )*

Under the Securities Exchange Act of 1934

QTS Realty Trust, Inc.

(Name of Issuer)

Class A common stock, $0.01 par value per share

(Title of Class of Securities)

74736A 103

(CUSIP Number)

Shirley E. Goza

General Counsel

QTS Realty Trust, Inc.

12851 Foster Street

Overland Park, Kansas 66213

(913) 312-5503

(Name, Address and Telephone Number of Person Authorized to Receive Notices and Communications)

October 15, 2013

(Date of Event Which Requires Filing of this Statement)

If the filing person has previously filed a statement on Schedule 13G to report the acquisition that is the subject of this Schedule 13D, and is filing this schedule because of §§ 240.13d-1(e), 240.13d-1(f) or 240.13d-1(g), check the following box:  ¨

Note: Schedules filed in paper format shall include a signed original and five copies of the schedule, including all exhibits. See Rule 13d-7 for other parties to whom copies are to be sent.

The information required on the remainder of this cover page shall not be deemed to be “filed” for the purpose of Section 18 of the Securities Exchange Act of 1934 (“Act”) or otherwise subject to the liabilities of that section of the Act but shall be subject to all other provisions of the Act (however, see the Notes).

2

ITEM 1. SECURITY AND ISSUER.

This Schedule 13D (the “Schedule 13D”) relates to the shares of Class A common stock, $0.01 par value per share (the “Class A common stock”), of QTS Realty Trust, Inc., a Maryland corporation (the “Issuer”). The Issuer is the general partner of QualityTech, LP, a Delaware limited partnership (the “Operating Partnership”). As disclosed in more detail in Item 5 below, the Reporting Person, as defined below, currently owns 6,517,000 Class A units of the Operating Partnership and 133,000 shares of the Issuer’s Class B common stock, $0.01 par value per share (“Class B common stock”). Pursuant to the terms of the Class A Units, on November 1, 2014, which is one year following the beginning of the first full calendar month following the closing of the Issuer’s initial public offering (the “IPO”), the Reporting Person may redeem the Class A units for cash or, at the Issuer’s election, shares of the Issuer’s Class A common stock. Pursuant to the Issuer’s Articles of Amendment and Restatement, the Class B common stock automatically converts into Class A common stock in certain circumstances and is convertible at any time into Class A common stock at the option of the holder.

The principal executive office of the Issuer is located at 12851 Foster Street, Overland Park, Kansas 66213

ITEM 2. IDENTITY AND BACKGROUND.

(a) This Schedule 13D is being filed by Chad L. Williams (the “Reporting Person”).

(b) The address of the Reporting Person is c/o QTS Realty Trust, Inc., 12851 Foster Street, Overland Park, Kansas 66213.

(c) The Reporting Person is the Chairman and Chief Executive Officer of the Issuer, whose address is listed in Item 1 above.

(d) – (e) During the last five years, the Reporting Person has not been convicted in a criminal proceeding (excluding traffic violations and similar misdemeanors) and was not a party to a civil proceeding of a judicial or administrative body of competent jurisdiction that as a result of such proceeding was or is subject to a judgment, decree or final order enjoining future violations of, or prohibiting or mandating activities subject to, federal or state securities laws or finding any violation with respect to such laws.

(f) The Reporting Person is a citizen of the United States of America.

ITEM 3. SOURCE AND AMOUNT OF FUNDS OR OTHER CONSIDERATION.

Prior to July 2013, the following Class A units and Class D units of the Operating Partnership were acquired, of which the Reporting Person is the beneficial owner:

In July 2013, the Reporting Person contributed $1,000 in personal funds to acquire 1,000 shares of common stock as part of the Issuer’s initial capitalization. Pursuant to a Share Redemption Agreement dated October 15, 2013, the Issuer repurchased the 1,000 shares issued to the Reporting Person in connection with the initial capitalization of the Issuer for the original purchase price of $1,000.

3

In September 2013, QTG entered into the Class B Stock Purchase Agreement dated as of September 25, 2013 with the Issuer pursuant to which QTG agreed to contribute 133,000 Class A units (that QTG received upon the automatic conversion of 133,000 Class D units of the Operating Partnership into Class A units on a one-for-one basis immediately prior to the consummation of the IPO) to the Issuer as consideration for the purchase of 133,000 shares of the Issuer’s Class B common stock. The Reporting Person is the manager and member of QTG. All of the 400,000 Class D units of the Operating Partnership owned by QTG automatically converted into Class A units on a one-for-one basis immediately prior to the consummation of the IPO. As a result of the disposition of the Class A units pursuant to the Class B Stock Purchase Agreement, QTG owns, as of the date of this report, 267,000 Class A units of the Operating Partnership.

Each outstanding share of Class B common stock entitles its holder to 50 votes on all matters on which Class A common stockholders are entitled to vote, including the election of directors, and holders of shares of Class A common stock and Class B common stock vote together as a single class. The Class B common stock is designed to give the holder thereof a right to vote that is proportional to such holder’s economic interest in the Issuer as if such holder had exchanged all of his Class A units for shares of Class A common stock, and does not provide any disproportionate voting rights. The Class B common stock automatically converts into Class A common stock in certain circumstances and is convertible at any time into Class A common stock at the option of the holder.

On October 15, 2013, pursuant to the terms of the Contribution Agreement dated October 15, 2013, the Reporting Person contributed to the Operating Partnership all of his ownership interest in QualityTech GP, LLC, the former general partner of the Operating Partnership, in exchange for 1,000 Class A units of the Operating Partnership.

The Class A units are redeemable for cash or, at the Issuer’s election, shares of Class A common stock on a one-for-one basis beginning on November 1, 2014, which is one year following the beginning of the first full calendar month following the closing of the Issuer’s IPO.

Pursuant to the terms of the Assignment and Assumption Agreement dated October 4, 2013 between the Reporting Person and Chad L. Williams, as Trustee of the Chad L. Williams October 2013 GRAT (the “GRAT”), the Reporting Person assigned 835,000 Class A units to the GRAT.

In addition, on October 15, 2013 (i) the Reporting Person purchased 47,619 shares of Class A common stock in the IPO and (ii) the Issuer granted 19,642 restricted shares of Class A common stock to the Reporting Person under the QTS Realty Trust, Inc. 2013 Equity Incentive Plan.

ITEM 4. PURPOSE OF TRANSACTION.

The Reporting Person acquired the shares of Class A common stock, Class B common stock and Class A units reported herein solely for investment purposes.

The following describes plans or proposals that the Reporting Person has with respect to the matters set forth in Item 4(a)-(j) of Schedule 13D:

(a) The Reporting Person entered into lock-up agreement with respect to the shares of Class A common stock and securities exchangeable or exercisable for shares of Class A common stock owned by the Reporting Person. The lock-up agreement restricts the direct or indirect sale of such securities for 180 days after the date of pricing of the IPO, which occurred on October 8, 2013, without the prior written consent of the underwriters. Following completion of the lockup period, the Reporting Person may hold, sell or otherwise dispose of the shares of Class A common stock, Class B common stock and Class A units, pursuant to federal and state securities laws and any other contractual obligations.

(b) Except as described in this Item 4, the Reporting Person does not have, as of the date of this Schedule 13D, any other plans or proposals that relate to or would result in any of the actions or events specified in clauses (a) through (j) of Item 4 of Schedule 13D. The Reporting Person may change his plans or proposals in the future. In determining from time to time whether to sell shares of Class A common stock reported as beneficially owned in this Schedule 13D (and in what amounts), to retain such securities or to purchase additional securities, the Reporting Person will take into consideration such factors as he deems relevant, including the business and prospects of the Issuer, anticipated future developments concerning the Issuer, existing and anticipated market conditions from time to time, general economic conditions, regulatory matters and other opportunities available to the Reporting Person. The Reporting Person reserve the right to

4

acquire additional securities of the Issuer in the open market, in privately negotiated transactions (which may be with the Issuer or with third parties) or otherwise, to dispose of all or a portion of his holdings of securities of the Operating Partnership or to change his intention with respect to any or all of the matters referred to in this Item 4.

ITEM 5. INTEREST IN SECURITIES OF THE ISSUER.

(a) As of the date of this report, the Reporting Person is deemed to beneficially own an aggregate of 6,717,261 shares of Class A common stock. As noted above, the shares of Class A common stock the Reporting Person is deemed to beneficially own is based upon the Reporting Person’s beneficial ownership of 67,261 shares of Class A common stock, 133,000 shares of Class B common stock (which are currently redeemable for a maximum of 133,000 shares of Class A common stock) and 6,517,000 Class A units of the Operating Partnership (which become redeemable on November 1, 2014 and may be redeemed by the Reporting Person for cash or, at the Issuer’s election, shares of the Issuer’s Class A common stock).

The Reporting Person’s holdings represent approximately 18.9% of the outstanding class of Class A common stock, based upon 35,489,774 shares of Class A common stock deemed outstanding upon the issuance of 6,650,000 shares of Class A common stock upon the redemption of the Class A units and the Class B common stock beneficially owned by the Reporting Person.

(b) Number of shares to which the Reporting Person has:

(c) Except as described in Item 3 above or elsewhere in this Schedule 13D, the Reporting Person has not effected any transactions in the shares of Class A common stock during the past 60 days.

(d) Not applicable.

(e) Not applicable.

ITEM 6. CONTRACTS, ARRANGEMENTS, UNDERSTANDINGS OR RELATIONSHIPS WITH RESPECT TO SECURITIES OF THE ISSUER.

The Reporting Person hereby references the disclosures contained in Item 4 of this Schedule 13D regarding the Contribution Agreement, Class B Stock Purchase Agreement and Assignment and Assumption Agreement and make the following additional disclosures:

Registration Rights Agreement

Pursuant to the Amended and Restated Registration Rights Agreement dated as of October 15, 2013, the Issuer has agreed to file a shelf registration statement with the Securities and Exchange Commission, once the Issuer is eligible, to register for resale the shares of Class A common stock that are held by the Reporting Person.

Lock-up Agreement

Pursuant to a Lock-Up Agreement which was entered into by the Reporting Person and the underwriters in connection with the Issuer’s IPO, the Reporting Person agreed not to dispose of the shares of Class A common stock held by the Reporting Person for a period of 180 days following the pricing of the IPO, which occurred on October 8, 2013, without the prior written consent of the representatives of the underwriters.

5

ITEM 7. MATERIAL TO BE FILED AS EXHIBITS.

6

SIGNATURE

After reasonable inquiry and to the best of my knowledge and belief, I certify that the information set forth in this statement is true, complete and correct.

Dated: October 25, 2013

7

Exhibit D

QTS Realty Trust, Inc.

Lock-Up Agreement

September 26, 2013

Goldman, Sachs & Co.

Jefferies LLC

c/o Goldman, Sachs & Co.

200 West Street

New York, NY 10282-2198

And

Jefferies LLC

520 Madison Avenue

New York, New York 10022

Re: QTS Realty Trust, Inc. - Lock-Up Agreement

Ladies and Gentlemen:

The undersigned understands that you, as representatives (the “Representatives”), propose to enter into an Underwriting Agreement (the “Underwriting Agreement”) on behalf of the several Underwriters named in Schedule I to such agreement (collectively, the “Underwriters”), with QTS Realty Trust, Inc., a Maryland corporation (the “Company”), and QualityTech, LP, a Delaware limited partnership, providing for a public offering of Class A common stock, $0.01 par value per share (the “Stock”) of the Company (the “Shares”) pursuant to a Registration Statement on Form S-11 to be filed with the Securities and Exchange Commission (the “SEC”).

In consideration of the agreement by the Underwriters to offer and sell the Shares, and of other good and valuable consideration the receipt and sufficiency of which is hereby acknowledged, the undersigned agrees that, during the period specified in the following paragraph (the “Stockholder Lock-Up Period”), the undersigned will not offer, sell, contract to sell, pledge, grant any option to purchase, make any short sale or otherwise dispose of any shares of Stock of the Company, or any options or warrants to purchase any shares of Stock of the Company, or any securities convertible into, exchangeable for or that represent the right to receive shares of Stock of the Company, whether now owned or hereinafter acquired, owned directly by the undersigned (including holding as a custodian) or with respect to which the undersigned has beneficial ownership within the rules and regulations of the SEC (collectively the “Undersigned’s Shares”). The foregoing restriction is expressly agreed to preclude the undersigned from engaging in any hedging or other transaction which is designed to or which reasonably could be expected to lead to or result in a sale or disposition of the Undersigned’s Shares even if such Shares would be disposed of by someone other than the undersigned. Such prohibited hedging or other transactions would include without

limitation any short sale or any purchase, sale or grant of any right (including without limitation any put or call option) with respect to any of the Undersigned’s Shares or with respect to any security that includes, relates to, or derives any significant part of its value from such Shares.

The Stockholder Lock-Up Period will commence on the date of this Lock-Up Agreement and continue for 180 days after the public offering date set forth on the final prospectus used to sell the Shares (the “Public Offering Date”) pursuant to the Underwriting Agreement; provided, however, that if (1) during the last 17 days of the Stockholder Lock-Up Period, the Company releases earnings results or announces material news or a material event or (2) prior to the expiration of the Stockholder Lock-Up Period, the Company announces that it will release earnings results during the 15-day period following the last day of the Stockholder Lock-Up Period, then in each case the Stockholder Lock-Up Period will be automatically extended until the expiration of the 18-day period beginning on the date of release of the earnings results or the announcement of the material news or material event, as applicable, unless the Representatives waive, in writing, such extension. The undersigned hereby acknowledges that the Company has agreed in Section 5(e) of the Underwriting Agreement to provide written notice of any event that would result in an extension of the Stockholder Lock-Up Period pursuant to this paragraph to the undersigned (in accordance with Section 13 of the Underwriting Agreement) and agrees that any such notice properly delivered will be deemed to have been given to, and received by, the undersigned. The undersigned hereby further agrees that, prior to engaging in any transaction or taking any other action that is prohibited by the terms of this provision during the period from the date hereof to and including the 34th day following the expiration of the Stockholder Lock-Up Period, it will give notice thereof to the Company.

If the undersigned is an officer or director of the Company, (1) the Representatives agree that, at least three business days before the effective date of any release or waiver of the foregoing restrictions in connection with a transfer of Stock, the Representatives will notify the Company of the impending release or waiver, and (2) the Company has agreed in Section 5(e)(ii) of the Agreement to announce the impending release or waiver by press release through a major news service at least two business days before the effective date of the release or waiver. Any release or waiver granted by the Representatives hereunder to any such officer or director shall only be effective two business days after the publication date of such press release. The provisions of this paragraph will not apply if (a) the release or waiver is effected solely to permit a transfer not for consideration and (b) the transferee has agreed in writing to be bound by the same terms described in this letter to the extent and for the duration that such terms remain in effect at the time of the transfer.

Notwithstanding the foregoing, the undersigned may transfer the Undersigned’s Shares (i) pursuant to and in accordance with the Underwriting Agreement; (ii) as a bona fide gift or gifts, provided that the donee or donees thereof agree to be bound in writing by the restrictions set forth herein, (iii) to any immediate family member or any trust for the direct or indirect benefit of the undersigned or the immediate family of the undersigned or any of their successors upon death or any partnership or limited liability company, the partners or members of which consist of the undersigned and one or more members of the undersigned’s immediate family, provided that the family member, the trustee of the trust, or the manager of the limited liability company, as applicable, agrees to be bound in writing by the restrictions set forth herein, and provided further that any such transfer shall

2

not involve a disposition for value, (iv) by will, other testamentary document or applicable laws of descent, or (v) with the prior written consent of the Representatives on behalf of the Underwriters. For purposes of this Lock-Up Agreement, “immediate family” shall mean any relationship by blood, marriage or adoption, not more remote than first cousin. In addition, notwithstanding the foregoing, if the undersigned is a corporation, partnership or limited liability company, the undersigned may transfer the capital stock of the Company to any direct or indirect affiliate, general or limited partner, member or shareholder of such corporation or to any investment fund, trust or other business entity controlled, managed by or under common control or management with the undersigned; provided, however, that in any such case, it shall be a condition to the transfer that the transferee execute an agreement stating that the transferee is receiving and holding such capital stock subject to the provisions of this Agreement and there shall be no further transfer of such capital stock except in accordance with this Agreement, and provided further that any such transfer shall not involve a disposition for value. The undersigned now has, and, except as contemplated by clause (i), (ii), (iii), (iv) or (v) above, for the duration of this Lock-Up Agreement will have, good and marketable title to the Undersigned’s Shares, free and clear of all liens, encumbrances, and claims whatsoever. The undersigned also agrees and consents to the entry of stop transfer instructions with the Company’s transfer agent and registrar against the transfer of the Undersigned’s Shares except in compliance with the foregoing restrictions.

In addition, nothing in this Lock-Up Agreement shall prohibit the undersigned from establishing a Rule 10b5-1 trading plan during the Stockholder Lock-Up Period; provided that (a) no transactions thereunder are made until after the expiration of the Stockholder Lock-Up Period and (b) no public disclosure of such plan shall be required or voluntarily made until after the expiration of the Stockholder Lock-Up Period.

Notwithstanding any other provision contained herein, the undersigned shall be permitted to make transfers, sales, tenders or other dispositions of Undersigned’s Shares pursuant to a tender offer for securities of the Company or other transaction, including, without limitation, a merger, consolidation or other business combination, involving a change of control of the Company (including, without limitation, entering into any lock-up, voting or similar agreement pursuant to which the undersigned may agree to transfer, sell, tender or otherwise dispose of Undersigned’s Shares in connection with any such transaction, or vote any Undersigned’s Shares in favor of any such transaction), provided that all Undersigned’s Shares subject to this agreement that are not so transferred, sold, tendered or otherwise disposed of remain subject to this agreement; and provided further that it shall be a condition of transfer, sale, tender or other disposition that if such tender offer or other transaction is not completed, any Undersigned’s Shares subject to this agreement shall remain subject to the restrictions herein.

Notwithstanding anything herein to the contrary, if (i) the closing of the public offering has not occurred prior to October 31, 2013, (ii) the Company earlier notifies the Representatives in writing that it does not intend to proceed with the public offering, (iii) the Underwriting Agreement (other than any provision thereof which is expressed to survive termination) shall terminate or be terminated prior to payment for and delivery of the Shares to be sold thereunder or (iv) a request for withdrawal of the registration statement relating to the public offering is filed with the SEC, this Lock-Up Agreement shall be of no further force or effect and the undersigned shall be released from all obligations hereunder.

3

The undersigned understands that the Company and the Underwriters are relying upon this Lock-Up Agreement in proceeding toward consummation of the offering. The undersigned further understands that this Lock-Up Agreement is irrevocable and shall be binding upon the undersigned’s heirs, legal representatives, successors, and assigns.