[2][3] Harper won a scholarship to Gresham's School, Holt, then attended Emmanuel College, University of Cambridge, where he read law and theology.
Harper was a curate at All Souls Church, Langham Place (London), when he received what Pentecostals and charismatics refer to as the Baptism of the Holy Spirit, a religious experience accompanied by speaking in tongues.
This put him at odds with the church's evangelical rector, John Stott, and Harper left All Souls in 1964 to found the Fountain Trust, an organisation dedicated to spreading the charismatic message.
Harper left Anglicanism in 1995 because of what he saw as the Church of England's increasing doctrinal laxity, particularly with regard to the ordination of women.
He wrote about his views on female ordination in the 1994 book Equal and Different and related his journey to Orthodoxy in The True Light (1994).