Saul ‘Canelo’ Alvarez will move up two weight divisions to challenge WBO world light-heavyweight champion Sergey Kovalev on 2 November.
Alvarez, cited as the world’s best-paid boxer, and bids to win a version of a world title in a fourth weight class.
He currently holds world titles in the 160lb middleweight division but will now seek global honours at 175lbs.
“This 2 November will be one of the biggest challenges of my career,” the 29-year-old Mexican tweeted.
“We’re going to make history together.”
Alvarez has only lost once as a professional so far – to Floyd Mayweather in September 2013 – in a 55-fight career.
He said Kovalev is “one the most powerful rivals” at light-heavyweight.
Russia’s Kovalev, 36, has been a force in the division since first winning a world title against Wales’ Nathan Cleverly in 2013.
He defeated Britain’s Anthony Yarde in August.