UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

WASHINGTON, D.C. 20549

SCHEDULE 13D

Under the Securities Exchange Act of 1934

(Amendment No. 4)*

Merus N.V.

(Name of Issuer)

Common Shares, nominal value €0.09 per share

(Title of Class of Securities)

N5749R100

(CUSIP Number)

Peter Haahr

Novo Holdings A/S

Tuborg Havnevej 19

Hellerup, Denmark DK-2900

+45 3527 6592

Copy to:

B. Shayne Kennedy, Esq.

Latham & Watkins LLP

650 Town Center Drive, 20^th Floor

Costa Mesa, CA 92626

Telephone: (714) 540-1235

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

July 24, 2018

(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 which is subject of this Schedule 13D, and is filing this statement because of Rule 13d-1(e), 13d-1(f) or 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(b) 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 (the “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).

CUSIP No.: N5749R100

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This amendment (“Amendment No. 4”) amends the Schedule 13D originally filed with the SEC on May 26, 2016, as subsequently amended by Amendment No. 1 filed with the SEC on June 2, 2016, by Amendment No. 2 filed with the SEC on March 3, 2017 and by Amendment No. 3 filed with the SEC on July 20, 2017 (collectively, the “Schedule”). All capitalized terms contained herein but not otherwise defined shall have the meanings ascribed to such terms in the Schedule.

Item 2. Identity and Background

Item 2 of the Schedule is amended and replaced in its entirety as follows for the purpose of updating the directors and executive officers of Novo Holdings A/S and the Foundation listed on Schedule I:

The name of each director and executive officer of both Novo Holdings A/S and the Foundation is set forth on Schedule I to this Amendment No. 4.

The residence or business address of each director and executive officer of both Novo Holdings A/S and the Foundation is set forth on Schedule I to this Amendment No. 4.

The Foundation is a Danish self-governing and profit-making foundation, whose objectives are to provide a stable basis for commercial and research activities undertaken by the group of Novo companies and to support scientific, humanitarian and social purposes through grants.

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Item 5. Interest in Securities of the Issuer

Item 5(a) of the Schedule is amended and replaced in its entirety as follows:

(a) Novo Holdings A/S beneficially owns 1,102,795 Common Shares (the “Novo Shares”), representing approximately 4.88% of the Issuer’s outstanding Common Shares, based upon 22,620,635 Common Shares outstanding as of March 31, 2018, as reported in the Issuer’s F-3 Registration Statement filed with the SEC on May 15, 2018.

Item 5(b) of the Schedule is amended and replaced in its entirety as follows:

(b) Novo Holdings A/S is a Danish limited liability company wholly owned by the Novo Nordisk Foundation. Novo Holdings A/S, through its Board of Directors (the “Novo Board”), has the sole power to vote and dispose of the Novo Shares. The Novo Board, currently comprised of Lars Rebien Sorensen, Steen Riisgaard, Francis Cuss, Jean-Luc Butel, Jeppe Christiansen and Viviane Monges, may exercise voting and dispositive control over the Novo Shares only with the support of a majority of the Novo Board. As such, no individual member of the Novo Board is deemed to hold any beneficial ownership or reportable pecuniary interest in the Novo Shares. Except as described in this Amendment No. 4, neither the Foundation nor any person listed on Schedule I has the power to direct the vote as to, or the disposition of the Novo Shares.

Item 5(c) of the Schedule is supplemented as follows:

(c) On July 19, 2018, Novo Holdings A/S sold 2,712 shares of the Issuer’s Common Shares in the open market through a broker’s transaction at a weighted average price of $24.026 per share.

On July 23, 2018, Novo Holdings A/S sold 4,910 shares of the Issuer’s Common Shares in the open market through a broker’s transaction at a weighted average price of $23.0479 per share.

On July 24, 2018, Novo Holdings A/S sold 300,000 shares of the Issuer’s Common Shares in a block trade at a price of $21.00 per share.

Item 5(e) of the Schedule is amended and replaced in its entirety, as follows:

(e) The Reporting Person ceased to be a beneficial owner of 5% or more of the Issuer’s Common Shares on July 24, 2018.

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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.

Schedule I

Information regarding each director and executive officer of both Novo Holdings A/S and the Novo Nordisk Foundation is set forth below.