William Saint-Clair

William Saint Clair may refer to:


 * William St. Clair (1410–1484 aka William Sinclair), 1st Earl of Caithness
 * William St Clair of Roslin (1700–1778), of the Clan Sinclair, 21st Baron of Roslin
 * William St Clair (1937–2021), British historian
 * William St Clair Grant (1894–1918), Scottish rugby player
 * William St. Clair Tisdall (1859–1928), Anglican priest