UFC Tonight announced the official booking on Wednesday, and UFC officials have confirmed to ESPN. The fight will be contested at 170 pounds and will take place inside the newly built T-Mobile Arena in Las Vegas.
McGregor (19-3) remains the UFC's official 145-pound featherweight champion. He won that title by defeating Jose Aldo in a 13-second knockout in December. With McGregor accepting his second consecutive fight outside the weight class, the UFC has booked an interim title fight between Aldo (25-2) and Frankie Edgar (20-4-1), which also will take place at UFC 200.
McGregor, 27, suffered the first loss of his UFC career to Diaz (19-10) earlier this month at UFC 196. Diaz submitted McGregor via rear-naked choke in the second round.
UFC president Dana White, appearing on Wednesday's edition of SportsCenter, explained how the rematch came together, saying he and UFC CEO Lorenzo Fertitta met with McGregor after UFC 196 to discuss what was next for him.
"He was obsessed -- obsessed with fighting Nate Diaz again," White said. "Obviously, Lorenzo and I tried to argue with him and said, 'Let's go back to 145 (pounds) and defend your title. Or if you really want the Diaz fight that bad, do it at 155 (pounds).' He wants the fight at 170.
"Even his coach tried to get him to get off the rematch and off the 170-pound fight," White said, referring to John Kavanagh, "but it's what he wanted."
The original bout came under unique circumstances. McGregor was originally scheduled to challenge 155-pound lightweight champion Rafael dos Anjos, but that fight was scratched 11 days before, when dos Anjos withdrew with a broken foot. Diaz agreed to fill in on short notice, and the bout was made at 170 pounds.
Aldo, 29, has been asking for a rematch since losing to McGregor at UFC 194. Fighting out of Rio de Janeiro, Aldo had recorded seven title defenses before the loss.
The interim title fight is a rematch of a championship fight that took place at UFC 156 in February 2013. Aldo defeated Edgar via unanimous decision. Edgar, who is a former UFC lightweight champion, has earned a second shot at the title on the heels of a five-fight winning streak, including wins over BJ Penn, Urijah Faber and Chad Mendes.
According to White, the winner of the interim title fight between Aldo and Edgar will definitely face McGregor next.
"Win, lose or draw in this fight against Nate Diaz, (McGregor) will go in and fight either Jose or Frankie," White said. "Whoever wins at UFC 200."
Also confirmed for UFC 200 is the return of former heavyweight champion Cain Velasquez (13-2) against Travis Browne (18-3-1). Welterweight Johny Hendricks (17-4), also a former champion, will take on Kelvin Gastelum (11-2).