MacCulloch joined the Gay Christian Movement in 1976, serving twice on its committee and briefly as honorary secretary. From 1978 to 1990 he tutored at Wesley College, Bristol, and taught church history in the department of theology at the University of Bristol. He interrupted his teaching to study for the Oxford Diploma in Theology (awarded 1987) at Ripon College Cuddesdon. In 1987 he was ordained a deacon in the Church of England and from 1987 to 1988 he served as a non-stipendiary minister at All Saints' Clifton with St John's in the Diocese of Bristol. However, in response to a motion put before the General Synod in 1987 by Tony Higton regarding the sexuality of clergy, he declined ordination to the priesthood and ceased to minister at Clifton.