There have been what feels like years of speculation about the fight, with much name-calling on both sides. But the two fighters have announced that it is indeed, on.
Yes, that’s right, a boxer with a 49-0 record facing a man who has never taken part in a professional boxing fight.
Anyway, here’s everything you need to know about the fight.
What date is the fight and at what time?
The fight is happening on Saturday 26 August. While the times haven’t been announced, it will certainly be a late night or very early start for viewers in the UK, so expect to be up well into Sunday 27 August, and possibly calling in sick on Monday 28.
Where is the fight taking place?
The bout will be housed in the T-Mobile arena on the Las Vegas Strip in Nevada. The venue has held major fights in the past, including UFC 202, in which McGregor beat Nate Diaz on points.
How can I watch it on TV?
Details are still to be confirmed but the fight will be a pay-per-view event, organised by Showtime Sports.
The price has not been decided, though it is expected to be at or near the $99.95 charged for Mayweather’s 2015 fight with Manny Pacquiao that drew a record 4.4 million pay-per-view buys.
“This is really an unprecedented event,” said Stephen Espinoza, who heads Showtime Sports. “Really we haven’t seen anything in modern history that resembles it, it’s impossible to predict how many sales this will do.”
What are their fighting records?
Mayweather retired in 2015 with an unblemished 49-0 professional boxing record.
He is widely regarded as one of the best defensive fighters ever, and prides himself on his ability to evade punishment with his skillful movement about the ring while making adjustments against opponents on the fly.
A win for Mayweather would move him ahead of former heavyweight great Rocky Marciano, who also retired with a perfect 49-0 career record.
McGregor, the UFC’s reigning lightweight champion and former featherweight champion, is known as much for his bravado as for his explosive knockout power inside an MMA octagon.
The 28-year-old Irishman became the first UFC fighter to hold two belts simultaneously when he knocked out Eddie Alvarez in New York last November for the lightweight championship.
The UFC stripped McGregor of his featherweight belt shortly after that fight when he announced he would be taking some time off after he and long-time partner Dee Devlin had their first baby in May.
Known for his devastating striking and highlight-reel knockouts, McGregor is also quick and irrational on his feet, but few would back him to beat one of the most complete boxers of all time.
What are the rules of the fight?
The fight will be held under boxing rules, presenting a huge challenge for mixed martial artists McGregor as he faces off against one of the greatest defensive boxers in history.
Adding to McGregor’s challenge, the fighters will be using 10-ounce boxing gloves instead of the smaller UFC gloves and he will not be allowed to use the leg kicks or takedowns that are used in mixed martial arts.
McGregor will weigh in at 154 pounds, UFC president Dana White told ESPN.
What are the odds?
Bookies immediately predicted a Mayweather win. William Hill put the veteran fighter at 1/11 favourite.
Oddsmaker Nick Bogdanovich said the odds would be even more lopsided if it wasn’t for the deluge of small bets expected to come in from UFC fans on their fighter.
“Realistically if we were just putting up a number and didn’t have to take bets on it, Floyd would be 1/100,” Bogdanovich said. “But this will be a very, very big betting fight for sure, one of the biggest ever.