Prosser was born on 10 June 1868. He was educated at Llandovery College in Llandovery, Carmarthenshire, west Wales, before entering Keble College, Oxford, with a history scholarship. He obtained a third-class degree in modern history in 1891 and was then ordained deacon in 1892 and priest in 1893. He served as assistant curate of Holy Trinity, Aberystwyth (1892–96) and Christ Church, Swansea (1896–1909) before being appointed vicar of Pembroke Dock in 1909. He was additionally appointed Archdeacon of St David's in 1920. In 1927, he was consecrated as Bishop of St David's, a post he held until his death on 28 February 1950. He was also Archbishop of Wales from 1944 to 1949. He was appointed an Honorary Fellow of Keble College in 1949.
Views on Ecumenism
Prosser believed strongly that the Anglican Church in Wales was the true Catholic Church in Wales and that both the Roman Catholic and Nonconformist Churches were no more than "Intruders", as evidenced by his statement in 1946 (which he repeated in May 1949):
"The Roman clergy and Noncomformist ministers are intruders… There may be historical excuse for their being here, but we cannot recognise their right to be here…"
- Drennan, Basil St G., ed. (1970). The Keble College Centenary Register 1870 – 1970. Keble College, Oxford. p. 70. ISBN 978-0-85033-048-9.
- "Prosser, Right Rev. David Lewis". Who Was Who, 1920–2008. Oxford University Press. December 2007. Retrieved 8 Oct 2009.
- Davies, Noel A. (2008). A History of Ecumenism in Wales 1956 – 1990. University of Wales Press, Cardiff. p. 47. ISBN 978-0-7083-2150-8.
| Bishop of St David's
| Archbishop of Wales