Crozier was born in Belfast, the son of Rev. John Baptist Crozier. Educated at Portora Royal School and Trinity College, Dublin and ordained in 1903, his first post was a curacy in Banbridge. He was later Rector of Celbridge, Vicar of St Ann's Dublin, a temporary chaplain to the Forces, Canon of Christ Church Cathedral, Dublin and finally (before his appointment to the episcopate) Archdeacon of Dublin. During his 17 months as a Temporary Chaplain to the Forces, he served in Gallipoli and was mentioned in despatches He had become a Doctor of Divinity.
He died in Dublin in February 1966.
- "Obituary: J. W. Crozier, Bishop Of Tuam". The Times. 16 February 1966. p. 14.
- "A New History of Ireland" Moody,T.W; Martin,F.X; Byrne,F.J;Cosgrove,A: Oxford, OUP, 1976 ISBN 0-19-821745-5
- "Ireland Civil Registration Indexes, 1845-1958," (:BIRTHS entry for John Winthorp Crozier; citing Belfast, Jan - Mar 1880
- Fox-Davies, Arthur Charles (1899). Armorial Families: A Directory of Some Gentlemen of Coat-Armour. p. 216. Retrieved 7 June 2017.
- Who was Who 1897-2007 London, A & C Black, 2007 ISBN 978-0-19-954087-7
- Church web site
- Crockford's Clerical Directory1940-41 Oxford, OUP,1941
- Information held at the Museum of Army Chaplaincy