EXHIBIT 32.2

CERTIFICATION

PURSUANT TO 18 U.S.C. SECTION 1350,

AS ADOPTED PURSUANT TO

SECTION 906 OF THE SARBANES-OXLEY ACT OF 2002

In connection with the Annual Report on Form 10-K of Nightstar Therapeutics plc (the “Company”) for the year ended December 31, 2018 as filed with the Securities and Exchange Commission on the date hereof (the “Report”), the undersigned, Senthil Sundaram, Chief Financial Officer of the Company, hereby certifies, pursuant to 18 U.S.C. Section 1350, that:

(1) The Report fully complies with the requirements of Section 13(a) or 15(d) of the Securities Exchange Act of 1934, as amended; and

(2)  The information contained in the Report fairly presents, in all material respects, the financial condition and results of operations of the Company.

/s/ Senthil Sundaram,

Senthil Sundaram,

Chief Financial Officer

(Principal Financial Officer)

Dated March 18, 2019