William Macdonald Sinclair, DD, FRGS (1850–1917), was an eminent Anglican priest and author in the late 19th and early 20th centuries.
He was born into an ecclesiastical family on 3 June 1850, educated at Repton and Balliol and ordained in 1876. His first post was as assistant minister at the Quebec Chapel, Marylebone after which he was resident chaplain to the Bishop of London. He was appointed vicar of St Stephen’s, Westminster in 1880 and Archdeacon of London in 1889. In 1892 he succeeded Walter Purton as editor of the Churchman, filling the post until 1901, when he was succeeded by Augustus Robert Buckland.
His last clerical appointment was as Rector of Shermanbury (1911–1915). An Honorary Chaplain to the King, he died on 4 December 1917.
He was elected to the London School Board as one of the representatives of the Westminster Division in 1885.
He was appointed Acting Chaplain to the 21st Middlesex (Volunteer) Battalion on 31 January 1900.