William Sinclair
William Sinclair may refer to:
Nobility
- William Sinclair, 1st Earl of Caithness, Scottish nobleman
- William Sinclair, 2nd Earl of Caithness, Scottish nobleman
- William Sinclair, 10th Earl of Caithness, Scottish nobleman
Politicians
- William Pirrie Sinclair, MP for Antrim and Falkirk Burghs
- W. E. N. Sinclair, Canadian barrister, solicitor and politician
- William Henry Sinclair, Canadian politician in the Legislative Assembly of the Northwest Territories
Religious figures
- William Sinclair (bishop), bishop of Dunkeld
- William Sinclair (priest), Scottish author and rector of Pulborough, Sussex
- William Sinclair (archdeacon of London), Anglican priest and author
- William Sinclair (United Irishmen), Irish revolutionary
Others
- William Sinclair (cricketer), Australian cricketer
- William Sinclair (general), US Army brigadier general
- William Sinclair (footballer), Scottish footballer
- William Sinclair (fur trader), chief factor of the Hudson's Bay Company
- William H. Sinclair Businessman; Union Officer
- William John Sinclair, American geologist and paleontologist
- William Angus Sinclair, Scottish philosopher
- Will Sinclair, a character in ''Angel in My Pocket''