 Demant was ordained as a deacon in 1919 and as a priest in 1920.He served curacies at St Thomas the Martyr's Church, Oxford; St Michael and All Angels Church, Summertown, Oxford; St Nicholas' Church, Plumstead, London; and All Saints' Church, Highgate, London.From 1929 to 1933, he was an assistant priest at St Silas Church, Kentish Town.