Viscount Thurso, of Ulbster in the County of Caithness, is a title in the Peerage of the United Kingdom.

[1] It was created on 11 June 1952 for the Scottish Liberal politician and former Secretary of State for Air, Sir Archibald Sinclair, 4th Baronet.

Thurso lost his seat in the House of Lords after the passing of the House of Lords Act 1999, but was elected to the House of Commons in 2001, thereby becoming the first hereditary peer of the United Kingdom allowed to sit in the Commons without first disclaiming his title; he held his seat until his defeat in the 2015 general election.

[3] The Sinclair baronetcy, of Ulbster in the County of Caithness, was created in the Baronetage of Great Britain in 14 February 1786 for the first Viscount's great-great-grandfather, the Scottish politician and writer John Sinclair.

The latter was the grandfather of the fourth Baronet, who was elevated to the peerage as Viscount Thurso in 1952.