Haye is the former undisputed cruiserweight wolrld champion
Britain's former world cruiserweight champion David Haye will take on Russia's WBA heavyweight champion Nikolay Valuev on 7 November.
The announcement ends speculation about who Haye's next opponent would be, following reports the Londoner had agreed a bout with Vitali Klitschko.
Haye, 28, is eight stones lighter and nine inches shorter than Valuev.
He said: "David only needed a slingshot and stone to flatten Goliath, my right hand generates more power than that."
Valuev, who is 7ft tall, has yet to be floored or knocked out in his 16-year professional career and has lost just once in 50 fights.
But Haye, who has also lost just once in his career, said: "I am thrilled to announce that my dream of becoming world heavyweight champion will be realised on 7 November, when I challenge the tallest and heaviest champion of all time.
"I can't wait to step into the ring and prove that size doesn't matter. Mark my words: I will be the first man to knock Nikolai Valuev out."
Haye revealed how he first saw Valuev fight when he was 16 at the Battersea Hall in London and recalled thinking at the time how difficult it would be to fight someone so big.
The 28-year-old has also admitted that it will be difficult to find sparring partners the same size as Valuev, making preparation for the fight even harder.
A venue for the contest has yet to be announced but the 02 Arena in London is rumoured to be in contention to stage the fight.
Haye had been scheduled to fight Klitschko's brother Wladimir in June but withdrew from the fight against the WBO and IBF champion because of a back injury.
That back injury has now healed and negotiations were underway with Wladimir's brother Vitali, the WBC champion, and Haye.
But Haye has decided to face Valuev, explaining that the conditions of the contract were more favourable.
"There were reports in the German press that I had signed to fight Vitali Klitschko in September, but those reports were never true," he added.
"There have been long and exhausting discussions about the clash, but unfortunately I could never put my name to the fight contract the Klitschkos offered.
"The level of disrespect they have shown me throughout has left me feeling insulted."
Having decided to fight Valuev instead of either of the Klitschko brothers, Haye has now been told he has burned his bridges with the the Ukrainian champions.
According to Bernd Bonte, the Klitschkos' manager, a deal was agreed and set to be signed for Haye and Vitali to meet - only for him to learn in the English media that the Londoner had changed his mind.
It now appears unlikely that Haye will meet either of the Klitschko brothers, even if he wins Valuev's WBA title.
"At the moment I would say there is zero chance," said Bonte, when asked whether the brothers would negotiate with Haye in the future.
"We discussed twice with the guy and he pulled out twice so why should we do it a third time? I would say, at the moment, no.
"We would be very reluctant to deal with Haye and [his manager Adam] Booth. Not again. Not a third time."
The only potential stumbling block to Haye fighting Valuev is a claim by John Ruiz - who has twice lost to the Russian - that he is the mandatory challenger.
In a letter to the WBA, the American's team said: "John Ruiz will not sit by and permit another delay so Valuev can have another interim fight, especially against an opponent who is not even rated by the WBA.
"John Ruiz has not agreed to permit any bout for the WBA heavyweight championship unless he is one of the participants, and he will take any and all legal action necessary to protect his interests."
Valuev's team believe they have already fulfilled their mandatory commitments by agreeing to face former champion Ruslan Chagaev.
However that fight was cancelled when Chagaev was declared medically unfit.