Gunn was born on December 25, 1973, in Ontario, Canada, into an Irish Traveller family from the Republic of Ireland and the United Kingdom.
Gunn made his professional boxing debut on April 28, 1989, Tucson, Arizona, winning by unanimous decision over Richard Palmer.
Gunn then put together a solid six-bout unbeaten streak, including a third round stoppage in a rematch against Gross, where he won three different titles.
He once again found himself in the limelight on July 11, 2009, when he challenged Ring Magazine and International Boxing Federation champion Tomasz Adamek.
[1][2] Gunn defeated Stewart with a KO in round 3, winning the vacant heavyweight bareknuckle boxing title.