The Reverend William Macdonald Sinclair (3 June 1850 - 4 December 1917) was a Church of England clergyman. The son of William Sinclair, Prebendary of Chichester Cathedral, he was educated at Repton School and Balliol College, Oxford. Ordained as a priest in 1876, he first served as curate of the Quebec Chapel, Marylebone, subsequently becoming resident chaplain to the Bishop of London. In 1880 he became vicar of St Stephen's, Westminster. In 1911 he left the capital to take up a clerical post in Sussex.