The promotion has been furiously working on a new main event this week, after Max Holloway, UFC 222's original headliner, was forced to pull out with an ankle injury. Holloway (19-3) was supposed to defend his title against No. 1 contender Frankie Edgar.
The UFC has found its replacement in Justino and Kunitskaya.
In addition to the main event, Edgar (22-5-1) is expected to remain on the card in a nontitle bout against undefeated contender Brian Ortega (13-0).
Justino (19-1) is coming off her first UFC title defense against Holly Holm on Dec. 30 in Las Vegas. UFC president Dana White had expressed interest in pairing Justino with bantamweight champion Amanda Nunes, but those plans are on hold for now.
Kunitskaya (10-3) is a former bantamweight champion in the all-female promotion Invicta FC. She has not fought in the UFC previously.
The UFC 222 pay-per-view event is scheduled to take place at T-Mobile Arena.