Hill International Inc. (HIL): James Mai’s Cornwall Capital Management Discloses Activist Stake

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

SCHEDULE 13D

Under the Securities Exchange Act of 1934

(Amendment No.     )*

Hill
International, Inc.

(Name of Issuer)

Common Stock, $0.0001 par value per share

(Title of Class of Securities)

431466101

(CUSIP Number)

Cornwall Capital Management LP

Attn: Ian D. Haft

570
Lexington Avenue, Suite 1001

New York, New York 10022

(917) 639-5438

With a
copy to:

Richard J. Birns, Esq.

Gibson, Dunn & Crutcher LLP

200 Park Avenue

New
York, New York 10166

(212) 351-4032

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

April 12, 2016

(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 the subject of this Schedule 13D, and is filing this schedule because of Sections 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
Section 240.13d-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).

This statement on Schedule 13D (this Schedule 13D)
relates to shares of common stock, par value $0.0001 per share (the Common Stock), of Hill International, Inc., a Delaware corporation (the Issuer). The Issuers principal executive offices are located at One Commerce
Square, 2005 Market Street, 17^th Floor, Philadelphia, Pennsylvania 19103.

(i) Cornwall Master LP, a Cayman Islands exempted limited partnership (Master), with respect to the shares of
Common Stock directly held by it;

(ii) Cornwall Capital Management LP, a Delaware limited partnership
(Cornwall), which serves as investment manager to Master, with respect to the shares of Common Stock directly held by Master;

(iii) Cornwall GP, LLC, a Delaware limited liability company (GP), which serves as the general partner of Master,
with respect to the shares of Common Stock directly held by Master;

(iv) CMGP, LLC, a Delaware limited liability company
(CMGP), which serves as the general partner of Cornwall, with respect to the shares of Common Stock directly held by Master; and

(v) James A. Mai, a citizen of the United States (Mr. Mai), who is the principal and Chief Investment Officer of
Cornwall, the managing member of GP and the managing member of CMGP, with respect to the shares of Common Stock directly held by Master. Mr. Mai disclaims beneficial ownership of the shares of Common Stock reported herein.

The Reporting Persons used
approximately $9,887,995 (including brokerage commissions) in the aggregate to purchase the shares of Common Stock reported in this Schedule 13D. The funds used to acquire the Common Stock reported herein were derived from general working capital
made in the ordinary course of business.

The Reporting Persons may from time to time and at any time in the future, depending on various factors, including, without limitation, the
outcome of any discussions referenced above, other investment opportunities available to the Reporting Persons, conditions in the securities markets and general economic and industry conditions, take such actions with respect to their investment in
the Issuer as they deem appropriate at the time including but not limited to: (i) acquiring additional Common Stock and/or other equity, debt, notes, other securities, including but not limited to derivative or other instruments that are based
upon or relate to the value of the Common Stock or the Issuer (collectively, Securities) in the open market or otherwise; (ii) disposing of any or all of their Securities in the open market or otherwise; (iii) nominating or
recommending candidates to serve on the board of directors of the Issuer; (iv) discussing the various potential alternatives and strategies regarding the Issuer with others, including but not limited to interested market and industry
participants; (v) entering into agreements or understandings with other shareholders of the Issuer with respect to the voting, holding and/or disposition of Securities; or (vi) proposing or considering any one or more of the actions
described in subsections (a) through (j) of Item 4 of Schedule 13D.

Each of the Reporting Persons may be deemed the beneficial owner of the Common Stock reported herein. Each of the Reporting Persons have the
shared power to vote or to direct the vote of (and the power to dispose or direct the disposition of) the Common Stock reported herein.

On April 22, 2016, the Reporting Persons entered into a Joint Filing Agreement pursuant to which they agreed to the joint filing on behalf
of each of them of this Schedule 13D (and any amendments thereto) with respect to the securities of the Issuer. Such Joint Filing Agreement is attached hereto as Exhibit 1.

Except for the matters described herein, no Reporting Person has any contract, arrangement, understanding or relationship with any person with
respect to any securities of the Issuer.

SIGNATURES

After reasonable inquiry and to the best of each of the undersigneds knowledge and belief, each of the undersigned, severally and not jointly, certified
that the information set forth in this statement is true, complete and correct.

Dated: April 22, 2016