Thomas Sinclair may refer to:
Thomas Sinclair (politician) (1857–1940), Northern Irish Member of Parliament
Thomas Sinclair Jr. (1841–1888), politician in Manitoba, Canada
Tom Sinclair (born 1957), American athlete
Tom Sinclair (footballer) (fl. 1904–1907), Scottish football goalkeeper
Tommy Sinclair (born 1921), English footballer
Thomas Sinclair (writer), a contributor to the British Dictionary of National Biography
Thomas Sinclair (died 1881), American businessman whose widow built the Brucemore mansion in Cedar Rapids, Iowa
Thomas Sinclair, Australian actor in silient films such as The Kelly Gang (1920)
Tom Sinclair, coxswain of Scottish lifeboat RNLB Emma Constance (ON 693)
Thomas Sinclair, fictional character in the Killzone video games
Albert Thomas Sinclair, American lawyer who corresponded with Archduke Joseph Karl of Austria about the Romani language