Josh Taylor will fight Jose Ramirez on May 22 in a bid to become only the second undisputed super-lightweight champion of the four-belt era.
Scotland's IBF and WBA champion Taylor (17-0, 13 KOs) will take on WBC and WBO title-holder Ramirez (26-0, 17 KOs) at a location and venue to be confirmed.
Taylor unified the IBF and WBA titles in October 2019, edging Regis Prograis by majority decision before making his first defence as a unified champion last September by stopping mandatory challenger Apinun Khongsong in the first round.
Pound-for-pound great Terence Crawford remains the only man to be an undisputed super-lightweight champion during the four-belt era, and Taylor hopes to make a little history of his own in becoming the first Scot to achieve that feat.
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He said: "I'm excited it's been finalised and over the line. I can't wait to get in there for the biggest fight of my career. Fighting for the undisputed title is something all boxers dream about."
Ramirez has been a world champion since March 2018 when he toppled Amir Imam via unanimous decision to win the vacant WBC strap.
He knocked out Maurice Hooker in July 2019 to unify world titles and defended his belts last August with a majority decision over former world champion Viktor Postol.
Ramirez, a proud son of Mexican immigrants who hails from Avenal, California, is an agent of social change in his community.
He's devoted his time and resources to myriad causes, including cancer research, water rights for area farmers, and Covid-19 relief for Central Valley field workers.
"I look forward to making history by becoming the first boxer of Mexican descent to hold all four major world title belts," Ramirez said.
"I dedicate this fight to the Central Valley farm workers, who are out there every day helping feed the world. This fight is big, but nothing is bigger than getting vaccinations to the farm workers right now in the Central Valley."
Top Rank chairman Bob Arum said: "This is the best boxing has to offer, two elite fighters in the prime of their careers colliding in a legacy-defining matchup for the undisputed championship of the world.
"It's a true 50-50 fight, one that the fans and both fighters demanded."