UFC officials announced the bout Wednesday night.
Gagnon (9-2) has fought twice in the Octagon, losing his promotional debut to Bryan Caraway last summer. He returned in September, bouncing back with a submission victory over Walel Watson at UFC 152.
The 28-year-old Canadian was supposed to have returned at UFC 158 in March, but was forced off the card due to injury.
Kimura (10-0) puts his spotless record on the line in what will be his sophomore UFC effort. The Hawaiian made his Octagon debut earlier this year at UFC 156, where he submitted Chico Camus.
UFC light heavyweight champion Jon Jones puts his belt on the line against Alexander Gustafsson in the UFC 165 main event.