Harrison picked up the trophy and £32,000 prize fee at the ExCel Arena in London
Audley Harrison kept his career alive with victory in Prizefighter but British heavyweight champion Danny Williams suffered a humiliating loss.
Former Olympic champion Harrison, 37, beat Scott Belshaw, Danny Hughes and Coleman Barrett in successive three-round bouts to claim the £32,000 prize.
After four defeats in eight contests, it was a must-win for Harrison.
Williams, 36, also needed a win but was repeatedly knocked down in his first bout by the unheralded Carl Baker.
The Sheffield-based Baker weighed in at over 20st and had too much power for Williams, who went down twice in the opening round and twice more in the second before rallying in the third, but it was too late.
Prizefighter sees eight heavyweights compete in four quarter-finals, followed by semis and a final, all over three rounds and in quick succession.
Heavyweight rivals Williams and Harrison were the big names and had been expected to meet in the final, giving Williams a chance for revenge over the 2000 Olympic gold medallist.
Williams won their first meeting in 2005 only to be stopped in the third round of their rematch a year later.
After spending much of the opening two rounds against Baker on the canvas he could not save himself despite a spirited fightback in the third.
The defeat at London's ExCel Arena sees Williams relinquish his British title and throws into serious doubt the future of a man who has a win over former undisputed world champion Mike Tyson on his record.
Harrison was struggling in the final before landing a superb left
Harrison stopped Northern Ireland's Belshaw after two rounds of his quarter-final, and was a comfortable points winner over Danny Hughes in his semi-final.
The Las Vegas-based fighter was struggling after a poor opening round in the final but landed a superb left to finish Barrett with one punch.
Harrison said: "Everyone thought the door was closed for me after I lost in December against Martin Rogan.
"But after these three performances, there's still hope for me and hope for Britain to have a world champion.
"I think I've now created an opportunity where hopefully I can achieve my goals. All roads lead to a world title, so I want to do whatever gets me to that the quickest way possible."
Barrett had beaten Welshman Scott Gammer in his quarter-final as all three judges gave it to the Irishman by 29-28 margins, and then had too much for Baker in the last four.