Smith is best known for his part in all four series of the BBC's The Thick of It as senior special adviser Glenn Cullen, from 2005 to 2012.
He also featured as Michael Rodgers, Director of Diplomacy at the Foreign Office, in the film spin off In the Loop.
[citation needed] In 2010 Smith played Clive in all 12 episodes of the BBC comedy Grandma's House, alongside his The Thick of It co-star Rebecca Front.
Smith further collaborated with Simon Amstell when he played Graham Watkins in the 2017 mockumentary, Carnage.
[citation needed] In October 2012, Smith compered a rally organised by the Trades Union Congress against government cuts.