Welby worked for 11 years in the oil industry for the French oil company Elf Aquitaine based in Paris, in 1984 becoming treasurer of the oil exploration group Enterprise Oil PLC in London. He retired from his executive position in 1987, when he said he sensed a calling from God to be ordained.
From 1989 to 1992, Welby studied theology and trained for the priesthood at Cranmer Hall and St John's College Durham before becoming a curate at Chilvers Coton with Astley (Nuneaton) from 1992 to 1995. He then became rector of St James' Church, Southam and later vicar of Ufton from 1995 to 2002.
In 2002, Welby was appointed a canon residentiary of Coventry Cathedral and the co-director for International Ministry at the International Centre for Reconciliation. In 2005, he was appointed Sub-Dean and Canon for Reconciliation Ministry.
Welby was appointed Dean of Liverpool Cathedral in December 2007 and was installed there on 8 December 2007.
Welby was consecrated at York Minster on 28 October 2011 and was enthroned as Bishop of Durham in Durham Cathedral on 26 November 2011.