Amir Khan will challenge the outstanding WBO welterweight champion Terence Crawford on April 20.
The 32-year-old rejected terms to finally meet his rival Kell Brook to instead pursue one of the world's finest fighters and what could prove his defining fight at either Las Vegas' MGM Grand or Madison Square Garden in New York.
Khan - last a world champion in 2012 - will intriguingly also again be trained by the respected Virgil Hunter after two victories with Joe Goossen.
With the fight venue and a British television broadcaster to be confirmed in the coming fortnight, Khan said: "It'll be nice to get back with Virgil. Joe was also a great trainer (but) I've had a great career with Virgil.
Crawford, 31, is widely considered one of the world's top three fighters having in 2017 unified all four light-welterweight world titles, and he said: "You could say this is my hardest fight.
"Amir Khan's still dangerous, still fast, still got the experience, been a welterweight longer than me. But we're not taking any shortcuts in this fight. My way to be able to adjust in the blink of an eye - fighting so many styles in my life; there's never been a fighter I couldn't figure out.
"(Past Khan victim) Zab Judah was past his prime (when they fought); right now I'm better than anyone he's faced before."
The American's promoter Bob Arum added: "Crawford's the best welterweight since Sugar Ray Leonard; he'd be comparable or maybe even a slight favourite against Sugar Ray Leonard. I really believe he matches up with that ability.
"Amir, in the United States, is known for never, ever having a poor performance. He's a gutsy fighter with skills of the top level; a master boxer with very, very fast hands. Every fight he's been in people want to see because he's a true warrior and gives a great account of himself."