UFC officials announced the 145-pound contest on Tuesday.
McGregor (15-2) is coming off a lightning rod-type performance in his hometown of Dublin, Ireland on Saturday. The 26-year-old contender cruised to a TKO victory over Diego Brandao in the first round of a sellout fight at O2 Arena.
The win improved McGregor's record in the UFC to 3-0 and was his first appearance in nearly a year due to ACL surgery. After the win, McGregor said fighting Poirier in Las Vegas, where he's never fought, would be "perfect."
Poirier (16-3) is coming off a second-round TKO over Akira Corassani in April. A 10-fight UFC veteran, Poirier is 8-2 in the Octagon with five finishes.
Fighting out of American Top Team in Coconut Creek, Florida, Poirier will take a three-fight win streak into the McGregor contest. He also posted a first-round knockout over Brandao when the two met in December at UFC 168.
ESPN.com ranks Poirier the No. 5 featherweight in the world.