Bishop Mason was born in North Shields in the diocese of Hexham and Newcastle in the north of England in 1962. After completing high school at St. Anselm’s Roman Catholic High School in North Shields, and Kings College in London, he worked in Turin and London until 1992.
His seminary formation took place in Rome at the Venerable English College. Then Bishop (later Cardinal) Cormac Murphy-O’Connor ordained him a deacon in 1997. He was ordained a priest in 1998 and obtained a Licentiate in Philosophy from the Pontifical Gregorian University.
He served as assistant priest at St John the Baptist parish in Purley and from 2001-2012 became a full time chaplain to St. Thomas’ & Guys Hospital Trust. In 2012 he became Pastoral Director of Allen Hall Seminary, in the neighboring Diocese of Westminster as well as Director of Ongoing Formation for the diocese of Southwark in southeast England. He then became Episcopal Vicar in Kent in 2014 and then Auxiliary Bishop of Southwark in 2016.