Mayweather's return to the ring has long been touted
Floyd Mayweather Jr has agreed to step out of retirement and fight lightweight champion Juan Manuel Marquez.
Mayweather has not fought since beating Briton Ricky Hatton in their December 2007 welterweight bout.
But the undefeated five-division champion will return to fight Mexico's three-weight champion Marquez in July.
"I left on top and I'm here to fight and reclaim what is mine," the 32-year-old Mayweather told a news conference at a Las Vegas hotel on Saturday.
"Lately I've been running seven, eight miles a day. I'm in tremendous shape.
"When it comes to fight time, I'll be ready physically and mentally. I just want to be the best that I can be."
News of the contest comes on the day of Hatton's fight with Manny Pacquiao, and Mayweather is already being linked with a match against the winner of the bout.
Hatton takes on Pacquiao - currently regarded as the best pound-for-pound fighter in the world - for the light-welterweight championship belt at the MGM Grand in Las Vegas on Saturday.
Should Hatton shrug off his underdog tag and defeat the Filipino boxer, and if Mayweather overcomes the 35-year-old Marquez on 18 July, a rematch of their 2007 fight in Las Vegas is sure to be on the cards.
Mayweather stopped Hatton in the 10th round on that occasion, confirming his tag as the best pound-for-pound boxer at that time.
A rematch could generate even more interest given Mayweather's father, Floyd Mayweather Sr, has pledged to continue to train Hatton against his son.