Sources close to the promotion confirmed the story with Bleacher Report on Thursday night.
The bout is a replacement for the originally scheduled main event between Chris Weidman and Lyoto Machida, which itself was a replacement for the planned main event between Weidman and Vitor Belfort. Weidman was forced to postpone his participation in the bout due to lingering knee issues, and it was ultimately moved to the main event of UFC 175 in July.
Sources close to the bout told Bleacher Report that Raphael Assuncao was the next likely contender for Barao's title. But Assuncao wasn't going to be healthy enough to fight by May, and his camp was pushing for a July or August fight date instead. With few other options remaining, UFC matchmaker Sean Shelby pulled the trigger and gave Dillashaw the title fight.
For the last nine years, Barao has remained undefeated, with his only career loss coming in his very first professional fight. Since then, he has become one of the very best fighters on the planet and currently ranks No. 3 in the world on the UFC's official pound-for-pound rankings. Once the interim bantamweight champion, he became the official belt holder when former champion Dominick Cruz was forced to go back on the shelf with another injury earlier this year.
Barao defeated Urijah Faber in his last bout. Dillashaw, meanwhile, is coming off a win over Mike Easton. He has only lost twice since joining the UFC, dropping his first official UFC bout to John Dodson in the finals of The Ultimate Fighter 14 and then losing to Assuncao last October.