Born to the Sinclair family, Lord Thurso was educated at Eton College before entering management roles in the tourism and hospitality industry.

He held the seat until he was defeated at the 2015 general election by the Scottish National Party (SNP) candidate, Paul Monaghan.

In 2016, Thurso returned to the House of Lords after winning a by-election to fill a vacancy among the remaining Liberal Democrat hereditary peers.

Following his father's death in 1995, he took his seat in the House of Lords as the 3rd Viscount Thurso, where he became spokesman on tourism and later on food matters.

He served as Liberal Democrat Scotland spokesperson under Charles Kennedy,[2] but was sacked by Sir Menzies Campbell.

[4] He lost his Caithness, Sutherland and Easter Ross seat at the 2015 general election to Paul Monaghan of the Scottish National Party (SNP).

As a patron of the Bluebell Railway 50th Anniversary Appeal, on 24 April 2009, at the railway's Horsted Keynes station Thurso carried out the ceremonial renaming of the Battle of Britain class locomotive named after his grandfather, Sir Archibald Sinclair, Secretary of State for Air during that battle.