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
See also
edit- William Sinclair (disambiguation), as "Saint Clair" is an archaic variant of "Sinclair"
- Saint Clair (disambiguation)
- William (disambiguation)
- Clair (disambiguation)