Campbell began preaching in May 1974, and preached his first sermon on Bible prophecy on 24 September 1978. He was officially ordained to the ministry by Dr Francis Thomas on 18 July 1988. He graduated from the University of London with a bachelor's degree in history, and from the Queen's University of Belfast with a Certificate in Biblical Studies. He held the post of head of religious studies at Newtownabbey Community High School near Belfast where he was subject to at least one Ministry of Education inspection because of concerns about his teaching methods. He held fiercely anti-Catholic views (referring to Catholics as worshipping a "wafer God") and used his website to disseminate these sentiments. He was the author of a number of Bible study books, and lectured throughout the United Kingdom, the United States, Canada, and Australia although his ministry centred in Ulster, and many of his messages dealt with the political situation there. Campbell had contact with the Christian Assemblies International.