Harrison was born in the United Kingdom. He served as a recce platoon commander for the British Army. He moved to the United States and started working as a construction manager in Sherwood, Oregon after being forced to surrender his guns to the UK government, while pursuing competitive shooting.
In 2009, Harrison finished second in Trooper Class in the 2009 MGM Ironman multi-gun competition. Being an amateur gunsmith, the guns he used during the competition were made by himself. Harrison worked for Crimson Trace at this time. In December 2011, Harrison gained US citizenship.
Harrison became the editor of RECOIL in January 2013 to bring a strong Second Amendment viewpoint to the magazine; he writes several articles for each issue as well.