UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

SCHEDULE 13G

Under the Securities Exchange Act of 1934

(Amendment No.     )*

GrubHub, Inc.

(Name of Issuer)

Common Stock, par value $0.0001

(Title of Class of Securities)

400110102

(CUSIP Number)

January 22, 2016

(Date of Event Which Requires Filing of this Statement)

Check the appropriate box to designate the rule pursuant to which this Schedule is filed:

¨ Rule 13d-1(b)

xRule 13d-1(c)

¨ Rule 13d-1(d)

The information required in 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).

Item 1(a) Name of issuer.

GrubHub, Inc.

Item 1(b) Address of issuer’s principal executive offices.

111 W. Washington St.,

Suite 2100

Chicago, IL 60602

Item 2(a) Name of person filing.

PAR Investment Partners, L.P.

PAR Group, L.P.

PAR Capital Management, Inc.

Item 2(b) Address or principal business office or, if none, residence.

PAR Capital Management, Inc.

One International Place, Suite 2041

Boston, MA 02110

Item 2(c) Citizenship.

State of Delaware

Item 2(d) Title of class of securities.

Common Stock, par value $0.001

Item 2(e) CUSIP No.

400110102

Item 3. If this statement is filed pursuant to §§240.13d–1(b) or 240.13d–2(b) or (c), check whether the person filing is a:

Not applicable

Item 4. Ownership.

Provide the following information regarding the aggregate number and percentage of the class of securities of the issuer identified in Item 1.

(a) Amount Beneficially Owned:

PAR Investment Partners, L.P. – 5,455,000

PAR Group, L.P. – 5,455,000

PAR Capital Management, Inc. – 5,455,000

(b) Percent of Class:

PAR Investment Partners, L.P. – 6.4%

PAR Group, L.P. – 6.4%

PAR Capital Management, Inc. – 6.4%

(c) (1) Number of shares as to which PAR Investment Partners, L.P. has:

(i) sole power to vote or to direct the vote 5,455,000

(ii) shared power to vote or to direct the vote 0

(iii) sole power to dispose or to direct the disposition of 5,455,000

(iv) shared power to dispose or to direct the disposition of 0

(2) Number of shares as to which PAR Group, L.P. has:

(i) sole power to vote or to direct the vote 5,455,000

(ii) shared power to vote or to direct the vote 0

(iii) sole power to dispose or to direct the disposition of 5,455,000

(iv) shared power to dispose or to direct the disposition of 0

(3) Number of shares as to which PAR Capital Management, Inc. has:

(i) sole power to vote or to direct the vote 5,455,000

(ii) shared power to vote or to direct the vote 0

(iii) sole power to dispose or to direct the disposition of 5,455,000

(iv) shared power to dispose or to direct the disposition of 0

Item 5. Ownership of 5 Percent or Less of a Class.

Not applicable

Item 6. Ownership of More than 5 Percent on Behalf of Another Person.

Not applicable

Item 7. Identification and Classification of the Subsidiary Which Acquired the Security Being Reported on by the Parent Holding Company or Control Person.

The sole general partner of PAR Investment Partners, L.P. is PAR Group, L.P. The sole general partner of PAR Group L.P., is PAR Capital Management, Inc. Each of PAR Group, L.P. and PAR Capital Management, Inc. may be deemed to be the beneficial owner of all shares held directly by PAR Investment Partners, L.P.

Item 8. Identification and Classification of Members of the Group.

Not applicable

Item 9. Notice of Dissolution of Group.

Not applicable

Item 10. Certification.

By signing below I certify that, to the best of my knowledge and belief, the securities referred to above were acquired and are held in the ordinary course of business and were not acquired and are not held for the purpose of or with the effect of changing or influencing the control of the issuer of the securities and were not acquired and are not held in connection with or as a participant in any transaction having that purpose or effect.

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.

Date: February 1, 2016

SCHEDULE 13G

Exhibit 99.1

Joint Filing Agreement

In accordance with Rule 13d-l(k) under the Securities and Exchange Act of 1934, as amended, the undersigned agree to the joint filing on behalf of each of them of a statement on Schedule 13G (including amendments thereto) with respect to the issuer’s Common Stock and further agree that this Joint Filing Agreement be included as an exhibit to such Schedule 13G. Each party to this Joint Filing Agreement expressly authorizes each other party to file on its behalf any and all amendments to such statement on Schedule 13G.

In evidence whereof, each of the undersigned, being duly authorized, has executed this Joint Filing Agreement as of February 1, 2016.