The success is the 2000 Olympic heavyweight boxing gold medallist's second in the Prizefighter concept following a British Heavyweights win in 2009, and saw the 41-year-old bounce back from a first-round mauling at the hands of David Price last year.
Harrison took home the trophy and a grand total of £36,000 in prize money (£32,000 as tournament winner and £2,000 for each knockout win) after stopping American Derric Rossy in the third and last round of the final.
Rossy was a surprise finalist after shocking compatriot and pre-tourney favourite Travis Walker then Londoner Ian Lewison with split decision wins.
Harrison dropped Denmark's Claus Bertino with a counter-hook just 33 seconds into their quarter final, setting up a last-four encounter with fellow 40-something and former Prizefighter winner Martin Rogan, who advanced with a third-round TKO over Polish slugger Albert Sosnowski.
Lewison - cheered on by a large and vocal support in the famed venue's balconies - pummelled German giant Timo Hoffmann for a two-minute stoppage before being outpointed by Brooklyn-born Rossy, while Harrison won every round in the eyes of all three judges in a disappointing clash with Northern Irishman Rogan.
Rossy entered the final with cuts to his eye and nose and after surviving one knockdown, was ultimately felled by 'A-Force' for a history-making second Prizefighter crown.
Also on the card, Team GB's London 2012 boxing captain Tom Stalker made the jump from amateur to professional with a solid first win over Kristian Laight in light-welterweight action.
Liverpool-born Stalker strung together good offence and showed promising ring presence on his way to taking all four rounds on the referee's scorecard and 'The Captain' will return to the ring for his second pro bout on March 30 at Liverpool's Echo Arena underneath Tony Bellew v Isaac Chilemba.