LIMITED POWER OF ATTORNEY FOR SECTION 16 REPORTING OBLIGATIONS

Know all by these presents, that the undersigned hereby makes, constitutes and
appoints each of Bryan Yoon, Senthil Sundaram, and Bethany Calagione, signing
singly and each acting individually, as the undersigned's true and lawful
attorney in fact with full power and authority as hereinafter described to:

(1)	execute for and on behalf of the undersigned, in the undersigned's capacity
as a director and an officer of Nightstar Therapeutics plc (the "Company"),
Forms 3, 4, and 5 (including any amendments thereto) in accordance with Section
16(a) of the Securities Exchange Act of 1934, as amended, and the rules
thereunder (the "Exchange Act");

(2)	do and perform any and all acts for and on behalf of the undersigned which
may be necessary or desirable to prepare, complete and execute any such Form 3,
4, or 5, prepare, complete and execute any amendment or amendments thereto, and
timely deliver and file such form with the United States Securities and Exchange
Commission (the "SEC") and any stock exchange or similar authority, including
without limitation the filing of a Form ID, Update Passphrase, or any other
application materials to enable the undersigned to gain or maintain access to
the Electronic Data Gathering, Analysis and Retrieval system of the SEC;

(3)	seek or obtain, as the undersigned's representative and on the undersigned's
behalf, information regarding transactions in the Company's securities from any
third party, including brokers, employee benefit plan administrators and
trustees, and the undersigned hereby authorizes any such person to release any
such information to such attorney in fact and approves and ratifies any such
release of information; and

(4)	take any other action of any type whatsoever in connection with the
foregoing which, in the opinion of such attorney in fact, may be of benefit to,
in the best interest of, or legally required by, the undersigned, it being
understood that the documents executed by such attorney in fact on behalf of the
undersigned pursuant to this Power of Attorney shall be in such form and shall
contain such terms and conditions as such attorney in fact may approve in such
attorney in fact's discretion.

The undersigned hereby grants to each such attorney in fact full power and
authority to do and perform any and every act and thing whatsoever requisite,
necessary, or proper to be done in the exercise of any of the rights and powers
herein granted, as fully to all intents and purposes as the undersigned might or
could do if personally present, with full power of substitution or revocation,
hereby ratifying and confirming all that such attorney in fact, or such attorney
in fact's substitute or substitutes, shall lawfully do or cause to be done by
virtue of this power of attorney and the rights and powers herein granted.  The
undersigned acknowledges that the foregoing attorneys in fact, in serving in
such capacity at the request of the undersigned, are not assuming nor relieving,
nor is the Company assuming nor relieving, any of the undersigned's
responsibilities to comply with Section 16 of the Exchange Act.  The undersigned
acknowledges that neither the Company nor the foregoing attorneys in fact assume
(i) any liability for the undersigned's responsibility to comply with the
requirements of the Exchange Act, (ii) any liability of the undersigned for any
failure to comply with such requirements, or (iii) any obligation or liability
of the undersigned for profit disgorgement under Section 16(b) of the Exchange
Act.

This Power of Attorney shall remain in full force and effect until the
undersigned is no longer required to file Forms 3, 4, and 5 with respect to the
undersigned's holdings of and transactions in securities issued by the Company,
unless earlier revoked by the undersigned in a signed writing delivered to the
foregoing attorneys in fact.

IN WITNESS WHEREOF, the undersigned has caused this Power of Attorney to be
executed as of this 30th day of October, 2018.


/s/ David A. Fellows
_____________________________

Name: David A. Fellows