American Mayweather, 40, posted a video on Twitter confirming the fight details with the message: "It's official."
He will go after Floyd Mayweather and he will try to knock him out
It is reported each fighter could earn as much as $100m (£78.4m) from the bout, which would be one of the richest in boxing history.
Mayweather, a former five-weight world champion and widely considered the best boxer of his generation, retired unbeaten in 2015 after 49 bouts.
That followed a successful defence of his WBC and WBA welterweight titles, a victory that equalled Rocky Marciano's career record of 49-0.
Mayweather retired for the first time in 2008 after 39 fights.
