Undefeated world champions Josh Taylor and Jose Ramirez will meet to decide the undisputed light-welterweight king in Las Vegas on May 22.
Taylor (17-0, 13 KOs) added the WBA belt to his IBF crown when he beat Regis Prograis via majority decision in the thrilling October 2019 World Boxing Super Series final.
The Scottish southpaw made short work of Apinun Khongsong in his first defence, stopping the challenger with a brutal first-round body shot.
American Ramirez (26-0 17 KOs) was, like Taylor, a 2012 Olympian but boasts more experience in the professional ranks.
He consolidated the WBC title by stopping then-WBO ruler Maurice Hooker inside six rounds in July 2019.
A points win over one-time Taylor victim Viktor Postol last August kept those belts in Ramirez's possession and it means all four of the major titles in the division will be on the line when the fighters meet in under three months' time.
"I'm excited it's finalised and over the line," Taylor said. "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 added he is confident he can make history for a boxer of Mexican lineage, with undisputed status similarly a target for Saul 'Canelo' Alvarez at super-middleweight this year.
"I look forward to making history by becoming the first boxer of Mexican descent to hold all four major world title belts," he said.
Promoter Bob Arum of Top Rank hailed "a true 50-50 fight" that "the fans and both fighters demanded".