Ashdown was educated at St. John's School, Leatherhead and Keble College, Oxford, his first post after ordination was as a curate at St Mary’s Portsea, Portsmouth. He was then a Chaplain and Lecturer at Lincoln Theological College and then the Perpetual Curate of St Aidan’s, West Hartlepool and after that Rector of Houghton-le-Spring. From 1948 he was the Provost of Southwark Cathedral. After his nomination on 15 March, he was consecrated to the Episcopate on 1 May 1957 as the 8th Bishop of Newcastle, a post he held for 16 years until his 2 October 1972 retirement. He died on Boxing Day 1977.