William Saint Clair may refer to:
William St. Clair (1410–1484 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 (cricketer) (1894–1918), Scottish cricketer and British Army officer William St Clair Grant (rugby union) (1853–1896), his father, Scottish rugby union player William St. Clair Tisdall (1859–1928), Anglican priest
See also William Sinclair (disambiguation), as "Saint Clair" is an archaic variant of "Sinclair" Saint Clair (disambiguation) William (disambiguation) Clair (disambiguation)