He is a Labour Life Peer, who has had several roles in the House of Lords ranging from a Government Whip to a Defence Spokesman.

He recently spent years as the Opposition Deputy Chief Whip; when Labour returned to power after the 2024 United Kingdom general election the incoming Starmer ministry allotted the deputy chief whip's position (Captain of the Yeomen of the Guard) to Margaret Wheeler, Baroness Wheeler.

The son of Arthur and Ellen Tunnicliffe, he was educated at Henry Cavendish School in Derby and University College, London, where he graduated with a Bachelor of Science in mathematics in 1965.

Tunnicliffe was chief executive of London Regional Transport from 1998 to 2000 and chairman of the United Kingdom Atomic Energy Authority from 2002 to 2004.

Tunnicliffe is Trustee of Homerton College, Cambridge and council member of Royal Holloway, University of London.