EXECUTION

UNDERWRITING AGREEMENT

Euro Pacific Canada Inc.

As Representative of the several Underwriters

130 King Street West, Suite 2820

Pacific Canada Inc. (the Representative ) and National Securities Corporation (collectively with the Representative, the Underwriters and each individually, an Underwriter ) understand that,

subject to the terms and conditions stated herein, Acasti Pharma Inc., a corporation incorporated under the Business Corporations Act (Qu bec) (the Company ), proposes to issue and sell to the Underwriters an

aggregate of 16,000,000 units of the Company (each, a Unit , and collectively, the Firm Units ). Each Unit shall be comprised of a fixed combination of one (1) Class A share in the capital of the Company

(a Unit Share ) and one (1) common share purchase warrant (each, a Warrant ). Each Warrant shall entitle its holder to acquire one Class A share in the capital of the Company (a Warrant

Share ) at a price of US$1.50 for a period of five (5) years following the First Closing Date (as defined in Section 2(3)). The Warrants shall be created and issued pursuant to a warrant indenture (the Warrant

Indenture ) to be entered into as of the First Closing Date between the Company and Computershare Trust Company of Canada (the Warrant Agent ). The Class A shares in the capital of the Company are generally referred

to herein as Common Shares .

Based on the foregoing, and subject to the terms and conditions contained in this

Underwriting Agreement (the Agreement ), the Underwriters severally and not jointly, in respect of their percentages set forth in Section 9 hereof, agree to purchase from the Company, and by its acceptance hereof, the Company

agrees to sell to the Underwriters, all but not less than all of the Firm Units on the First Closing Date for a purchase price of US$1.25 (the Offering Price ) per Firm Unit, being an aggregate purchase price of US$20,000,000

against delivery of such Firm Units.

In addition, the Company proposes to grant to the Underwriters, in respect of their percentages set

forth in Section 9 hereof, an option (the Over-Allotment Option ), exercisable in whole or in part at any time prior to 5:00 p.m. (Montr al time) on the day that is the 30th day following the First Closing Date, to

purchase up to an additional 2,400,000 Units (the Additional Units and collectively with the Firm Units, the Offered Units ) representing up to 15.0% of the aggregate number of Firm Units, at the Offering Price

and upon the terms and conditions set forth herein for the purposes of covering over-allotments and for market stabilization purposes. The aforesaid Offered Units, Unit Shares, Warrants and Warrant Shares are collectively referred to herein as the

Securities . The Securities shall have the material attributes described in and contemplated by the Prospectuses which are referred to below.

(1) The Company has prepared and filed with the securities regulatory

authorities (the Canadian Commissions ) in each of the provinces of British Columbia, Alberta, Manitoba, Ontario and Qu bec (collectively, the Qualifying Jurisdictions ) a preliminary short form base shelf

prospectus dated October 16, 2013 relating to the distribution of up to US$150,000,000 of Common Shares, warrants, and units of the Company (the Shelf Securities ) pursuant to applicable securities laws of the Qualifying

Jurisdictions and the respective rules, regulations, blanket rulings, orders and notices made thereunder and the local, uniform, national and multilateral instruments and policies adopted by the Canadian Commissions in the Qualifying Jurisdictions

(collectively, as applied and interpreted, the Canadian Securities Laws ) and in accordance with Multilateral Instrument 11-102 Passport System ( MI 11-102 ) and National Policy 11-202 Process for

Prospectus Reviews in Multiple Jurisdictions ( NP 11-202 , and together with MI 11-102, the Passport System ). Such preliminary short form base shelf prospectus relating to the distribution of the Shelf

Securities, including any documents incorporated by reference therein and any supplements or amendments thereto, is herein called the Canadian Preliminary Base Prospectus. The Company has prepared and filed the Canadian

Preliminary Base Prospectus pursuant to National Instrument 44-101 Short Form Prospectus Distributions and National Instrument 44-102 Shelf Distributions, the Shelf Procedures . The Autorit des

march s financiers (Qu bec) (the Principal Regulator ) has issued a receipt for the Canadian Preliminary Base Prospectus and the Company has satisfied the conditions in MI 11-102 to the deemed issuance of a receipt by

the Canadian Commissions for the Canadian Preliminary Base Prospectus in each of the other Qualifying Jurisdictions.

(2) The Company has also prepared

and filed with the United States Securities and Exchange Commission (the SEC ) pursuant to the Canada/United States Multi-Jurisdictional Disclosure System adopted by the Canadian Commissions and the SEC (the

MJDS ), a registration statement on Form F-10 (Registration No. 333-191907) for the registration of the offering of the Shelf Securities under the United States Securities Act of 1933, as amended (together with the rules and

regulations promulgated thereunder, the Securities Act ), including the final short form base shelf prospectus dated October 25, 2013 relating to the distribution of the Shelf Securities (including any documents incorporated

therein by reference and any supplements or amendments thereto, the Canadian Final Base Prospectus ), pursuant to the Shelf Procedures, omitting the Shelf Information (as hereinafter defined) in accordance with the rules and

procedures set forth in NI 44-102 with such deletions therefrom and additions or changes thereto as are permitted or required by Form F-10 and the applicable rules and regulations of the SEC. The Company has also prepared and filed with the SEC an

Appointment of Agent for Service of Process and Undertaking on Form F-X at the time of the filing of the registration statement on Form F-10 (the Form F-X ).

(3) In addition, the Company (a) has prepared and filed with the SEC (i) a notice of clearance relating to the Canadian Final Base Prospectus issued

by the Autorit des march s financiers, the securities regulator in Quebec, Canada, for the U.S. Registration

Statement on Form F-10 (the prospectus in the U.S. Registration Statement on Form F-10, including the documents incorporated by reference therein and any supplements or amendments thereto when it

became effective pursuant to Rule 467(b) under the U.S. Securities Act on October 28, 2013 (the Effective Date ), is referred to herein as the U.S. Base Prospectus ), (ii) the preliminary prospectus

supplement dated November 26, 2013 specifically relating to the Offered Units, pursuant to General Instruction II.L of Form F-10, including the documents incorporated by reference therein (together with the U.S. Base Prospectus is hereinafter

referred to as the U.S. Preliminary Prospectus and (b) will prepare and file, as promptly as possible and in any event (i) not later than 11:00 p.m. (Montr al time) on November 27, 2013, with the Canadian

Commissions in the Qualifying Jurisdictions, in accordance with the Shelf Procedures, a prospectus supplement setting forth the Shelf Information (including any documents incorporated therein by reference and any supplements or amendments thereto,

the Canadian Prospectus Supplement , and together with the Canadian Final Base Prospectus, the Canadian Prospectus ), and (ii) within one business day of such filing with the Canadian Commissions, with the

SEC pursuant to General Instruction II.L, of Form F-10, the Canadian Prospectus Supplement (with such deletions therefrom and additions thereto as are permitted or required by Form F-10 and the applicable rules and regulations of the SEC) (the

U.S. Prospectus Supplement , and together with the U.S. Base Prospectus, the U.S. Prospectus ). The information, if any, included in the Canadian Prospectus Supplement that is omitted from the Canadian Final Base

Prospectus for which a final receipt has been obtained from the Canadian Commissions, but that is deemed under the Shelf Procedures to be incorporated by reference into the Canadian Final Base Prospectus as of the date of the Canadian Prospectus

Supplement, is referred to herein as the Shelf Information.

(4) The registration statement on Form F-10, including any amendment

thereof on or prior to the Effective Date and including the exhibits thereto, the documents incorporated or deemed to be incorporated by reference therein and any information deemed to be a part thereof at the Effective Date for purposes of

Section 10 under the Securities Act and including the Shelf Information, is herein called the Registration Statement.

Canadian Preliminary Base Prospectus and the U.S. Preliminary Prospectus, including the documents incorporated by reference therein and any supplements or amendments thereto that omit the Shelf Information are herein collectively sometimes referred

to as the Preliminary Prospectuses. The U.S. Prospectus and the Canadian Prospectus are hereinafter collectively sometimes referred to as the Prospectuses. The U.S. Prospectus Supplement and the Canadian

Prospectus Supplement are hereinafter collectively sometimes referred to as the Prospectus Supplements.

(6) Any amendment or

supplement to the U.S. Prospectus or the Canadian Prospectus (including any document incorporated by reference therein), that may be filed by or on behalf of the Company with the Canadian Commissions in the Qualifying Jurisdictions or with the SEC

after the Canadian Prospectus Supplement and the U.S. Prospectus Supplement have been filed and prior to the expiry of the period of distribution of the Offered Units, is referred to herein collectively as the Supplementary

(7) As used herein, the Applicable Time is 9:00 a.m. (New York time) on November 27,

2013. As used herein, a free writing prospectus has the meaning set forth in Rule 405 under the Securities Act, and a Time of Sale Prospectus means the U.S. Preliminary Prospectus together with the information

and the free writing prospectuses, if any, and each road show (as defined in Rule 433 under the Securities Act), if any, related to the offering of the Offered Units contemplated hereby that is a written communication (as

defined in Rule 405 under the Securities Act) (each such road show, a Road Show ) identified in Schedule A hereto.

the terms Registration Statement, Preliminary Prospectuses, Time of Sale Prospectus and Prospectuses shall include the documents incorporated and deemed to be incorporated by reference therein (the

Incorporated Documents ), including, unless the context otherwise requires, the documents, if any, filed as exhibits to such Incorporated Documents.

(9) All references in this Agreement to the Registration Statement, the U.S. Preliminary Prospectus or the U.S. Prospectus shall include any copy thereof

filed with the SEC pursuant to its Electronic Data Gathering, Analysis and Retrieval System ( EDGAR ). All references in this Agreement to Financial Statements (as defined in Section 3(o)) and schedules and other

information which are contained, included or stated in the Registration Statement, the Time of Sale Prospectus or the U.S. Prospectus (and all other references of like import) shall be deemed

to mean and include all such Financial Statements and schedules and other information which is or is deemed to be incorporated by reference in the Registration Statement, the Time of Sale Prospectus or the U.S. Prospectus, as the case may be; and

all references in this Agreement to amendments or supplements to the Registration Statement, the Time of Sale Prospectus or the U.S. Prospectus, as the case may be, shall be deemed to mean and include the filing of any document under the United

States Securities Exchange Act of 1934, as amended (together with the rules and regulations promulgated thereunder, the Exchange Act ) or otherwise that is or is deemed to be incorporated by reference in the Registration Statement,

the Time of Sale Prospectus or the U.S. Prospectus, as the case may be.

(10) As used herein, business day shall mean a day on which

each of the NASDAQ Capital Market ( NASDAQ ) and the TSX Venture Exchange ( TSXV ) is open for trading. The terms herein, hereof, hereto,

hereinafter and similar terms, as used in this Agreement, shall in each case refer to this Agreement as a whole and not to any particular section, paragraph, sentence or other subdivision of this Agreement. The term

or, as used herein, is not exclusive.

(11) The Underwriters shall offer the Offered Units for sale to the public directly and through other

duly registered investment dealers and brokers in the Qualifying Jurisdictions and the United States only as permitted by applicable law and upon the terms and conditions set forth in the Prospectuses and this Agreement. The Underwriters agree that

they will not, directly or indirectly, distribute the Registration Statement, the Time of Sale Prospectus, or the Prospectuses or publish any prospectus, circular, advertisement or other offering material in any jurisdiction other than the

Qualifying Jurisdictions or such states of the United States in which the Securities are duly qualified under United States

federal and applicable United States state securities laws, in such manner as to require registration of the Securities or the filing of a prospectus or any similar document with respect to the

Securities by the Company therein or subject the Company to ongoing periodic reporting obligations in such jurisdiction pursuant to the securities laws of such jurisdiction. The Underwriters agree that each of the Underwriters that is not registered

as a broker-dealer under Section 15 of the Exchange Act, will not offer or sell any Offered Units in, or to persons who are nationals or residents of, the United States other than through one of its United States registered broker-dealer

affiliates or otherwise in compliance with Rule 15a-6 under the Exchange Act. Sales of the Offered Units in the Qualifying Jurisdictions may be made only by or through a dealer appropriately registered under applicable Canadian Securities Laws or in

circumstances where an exemption from the Canadian registered dealer requirements is available. Notwithstanding the foregoing provisions of this paragraph, an Underwriter will not be liable to the Company under this Agreement with respect to a

default by another Underwriter under this paragraph.

The Company hereby confirms

its agreement with the Underwriters concerning the purchase and sale of the Offered Units as follows:

(1) Public Offering of the Offered

Units. The Representative hereby advises the Company that the Underwriters intend to offer for sale to the public, initially on the terms set forth in the Time of Sale Prospectus and each Prospectus, their respective portions of the Offered

Units as soon after this Agreement has been executed as the Representative, in its sole judgment, has determined is advisable and practicable. Following the First Closing Date, after the Underwriters have made a reasonable effort to sell all of the

Offered Units at the Offering Price, the purchase price of the Offered Units may be decreased by the Underwriters and may be further changed from time to time to an amount not greater than the Offering Price, and the compensation realized by the

Underwriters will be decreased by the amount that the aggregate price paid by purchasers for the Offered Units is less than the gross proceeds paid by the Underwriters to the Company.

(2) Underwriters Commission. In consideration of the Agreement of the Underwriters to purchase the Offered Units and to offer them to the

public, the Company agrees to pay to the Underwriters (a) at the First Closing Date (as defined in Section 2(3)) an underwriting fee equal to 3% of the gross proceeds from the sale of the Firm Units to those purchasers agreed to by the

Representative and the Company, and 6% of the gross proceeds from the sale of the Firm Units to all other purchasers; and (b) at the Option Closing Date (as defined in Section 2(4)) an underwriting fee equal to 6% of the gross proceeds

from the sale of the Additional Units (the Underwriters Commission ). The Underwriters Commission may be deducted by the Underwriters from the proceeds of sale of the Firm Units on the First Closing Date or the proceeds

of sale of the Additional Units on the Option Closing Date, as applicable. In addition, the Company agrees to pay to the Underwriters, and in the manner specified by the Representative, all fees, disbursements and expenses incurred by the

Underwriters in accordance with the provisions in Section 5 hereof.

(3) The First Closing Date in respect of the Firm Units. Payment