[1] He studied English literature at the University of Southampton, graduating with a Bachelor of Arts (BA) degree in 1980.

[2][3] He then underwent teacher training at Magdalen College, Oxford, completing his Postgraduate Certificate in Education (PGCE) in 1981.

[1] In 1985, Mounstephen entered Wycliffe Hall, Oxford, an Evangelical Anglican theological college, to train for ordained ministry.

[1] In 1998, Mounstephen joined the Church Pastoral Aid Society (CPAS) and served in a number of roles.

[2] In January 2007, Mounstephen returned to parish ministry as chaplain (the senior minister) of St Michael's Church, Paris.

[9] On 1 July 2012, it was announced that Mounstephen would be the next executive leader of the Church Mission Society (CMS) in succession to Tim Dakin.