Amir Khan's light-welterweight unification showdown with Zab Judah will take place at the Mandalay Bay Center in Las Vegas.
The fight, scheduled for July 23, was officially confirmed via a televised press conference - with Khan's WBA belt and Judah's IBF strap on the line.
And Khan is relishing the chance to add to titles against the battle-hardened Judah.
"I'm excited to have the opportunity to unify the 140-pound division which always has been a dream of mine," said Khan.
"Fighting Zab was the toughest option my team presented to me, but a true champion is up for any challenge. I already was in training camp because it doesn't matter who I fight; I will train hard no matter who it is because I want to be the best."
Having already dominated at welterweight, Judah is confident he can now clean up in the 10st division.
He added: "I got what I wanted, so I am happy. Now it's time to go work. I've been praying on this fight.
"My goal is to be undisputed champion at two weights. I did it at 147 and I'm gonna do it at 140 starting with Amir Khan. I'm gonna work hard. I'm very experienced, so whichever way he brings the fight, I can deal with it and take it from him."
Kathy Duva, chief executive of promoter Main Events, said Judah was desperate to make a deal happen.
"In the end, Zab and Main Events decided to stop quibbling about a few percentage points and get the fight into the ring. Zab's real upside will come after he wins the fight and moves on to an even bigger payday," said Duva.
"It is an intriguing fight on many levels. Both fighters have engaging personalities and exciting styles. As a promoter, I couldn't be happier about this opportunity. As a fan, I can't want to see the fight."
The 24-year-old Khan beat Paul McCloskey in April and had been linked with fights against either Timothy Bradley or Erik Morales.
Judah, 33, beat Junior Witter in 2000 and was involved in a stormy bout with Kostya Tszyu, which ended up with him throwing a stool.
He has also lost to Carlos Baldomir, Floyd Mayweather and Miguel Cotto.