Saul 'Canelo' Alvarez says he has signed a "historic" contract after agreeing a £278m ($365m) deal with streaming service DAZN.
The Mexican, who holds the WBA and WBC world middleweight titles, has signed a five-year, 11-fight deal that could be the most lucrative in sports history.
The 28-year-old said he was "humbled" to be selected for the contract.
Alvarez's first bout of the deal sees him step up to super-middleweight to face Rocky Fielding on 15 December.
"Being part of this historic deal will require me to prepare myself even more and offer fans even better performances," added Alvarez, who joined Britain's Fielding in New York on Wednesday to promote their fight at Madison Square Garden.
"At the same time, I am humbled to be selected to lead this new vision for the sport of boxing, which will without a doubt be for the benefit of the fans."
Alvarez's new contract is being described as the biggest in sports history by ESPN.
While it would eclipse the 13-year, $325m (then £208m) contract baseball's Giancarlo Stanton signed in 2014, when broken down on an annual basis he will earn less than the likes of Barcelona footballer Lionel Messi, who has an annual salary of $84m (£64m) according to Forbes.
However, it will earn him more than £1m a week over the five years and Alvarez - beaten only by Floyd Mayweather in a 53-fight career - can increase his earnings if DAZN achieve pre-determined subscription targets.
The streaming service charges $9.99 (£7.60) a month rather than one-off, pay-per-view fees.
Canelo was most recently aligned with US broadcaster HBO but the network announced it would move away from live boxing coverage at the end of 2018.
His last bout - a win in a rematch with Gennady Golovkin on 15 September - generated HBO an estimated $121m (£92m).
DAZN - owned by the Perform Group - launched in Austria, Germany, Japan and Switzerland in August 2016 and moved into the US market this year.
Anthony Joshua's defence of his IBF, WBO and WBA world heavyweight titles against Alexander Povetkin provided its first boxing event streamed in the US in September.