John Archibald Sinclair, 3rd Viscount Thurso (born September 10, 1953), known as John Thurso, is a British businessman and Liberal Democrat politician. His right as a herditary peer to sit in the House of Lords was abolished in 1999, but at the UK general election, 2001 he was elected to the House of Commons and became the first hereditary peer allowed to sit in the Commons without first renouncing his title.

His grandfather, the 1st viscount, was the Liberal Party leader Archibald Sinclair. He represents Caithness, Sutherland & Easter Ross, the seat formerly held by his grandfather.

{| border="2" align="center" |width="30%" align="center"|Preceded by:
Robin MacDonald Sinclair |width="40%" align="center"|Viscount Thurso |width="30%" align="center"|Followed by:
Current incumbant |}