William Sinclair may refer to:
Nobility William Sinclair, 1st Earl of Caithness (1410–1484), Scottish nobleman William Sinclair, 2nd Earl of Caithness (1459–1513), Scottish nobleman William Sinclair, 10th Earl of Caithness (1727–1779), Scottish nobleman
Politicians William Pirrie Sinclair (1837–1900), MP for Antrim and Falkirk Burghs W. E. N. Sinclair (1873–1947), Canadian barrister, solicitor and politician William Henry Sinclair (1864–1902), Canadian politician in the Legislative Assembly of the Northwest Territories
Religious figures William Sinclair (bishop) (died 1337), bishop of Dunkeld William Sinclair (priest) (1804–1878), Scottish author and rector of Pulborough, Sussex William Sinclair (archdeacon of London) (1850–1917), Anglican priest and author William Sinclair (United Irishmen) (died 1830), Irish revolutionary
Others William Sinclair (cricketer) (1846–1869), Australian cricketer William Sinclair (general) (1835–1905), US Army brigadier general William Sinclair (footballer) (born 1934), Scottish footballer William Sinclair (fur trader) (1790s–1868), chief factor of the Hudson's Bay Company William H. Sinclair (1838–1897) Businessman; Union Officer William John Sinclair (1877–1935), American geologist and paleontologist William Angus Sinclair (1905–1954), Scottish philosopher Will Sinclair, a character in Angel in My Pocket William C. Sinclair, Co-CEO J.P. Morgan U.S. Private Bank
See also William Saint-Clair (disambiguation), "Saint-Clair" is a variant of "Sinclair" Sinclair (disambiguation) William (disambiguation)