He was the Liberal Democrat Member of Parliament (MP) for North Norfolk from 2001 to 2019, and was the chair of the Science and Technology Select Committee from 2017 to 2019.

[3] A meeting with Shirley Williams in Parliament at this time, shortly after the formation in 1981 of the Social Democratic Party (SDP), spurred Lamb into front line active politics and he was elected to Norwich City Council where he led the Liberal Democrat group until he stood down in 1991 in order to pursue his Westminster ambitions.

He was finally elected in 2001, which was his third attempt for the seat; narrowly defeating the incumbent Conservative MP David Prior by 483 votes.

He was re-elected in 2005 with a significantly increased majority of 10,606 votes, despite a campaign by the Conservatives and their candidate Iain Dale to unseat him in what was one of their foremost target seats.

Following the 2005 general election, Lamb was promoted and appointed Liberal Democrat Trade spokesman (2005–2006), securing the endorsement of the Liberal Democrat Spring 2006 Conference for a policy to partially privatise the Royal Mail, and to use the proceeds to invest in a publicly owned Post Office network.

In March 2006, he moved to the post of Chief of Staff to the newly elected leader, Sir Menzies Campbell.

Following the formation of the Conservative-Liberal Democrat coalition government in May 2010, Lamb was appointed a Parliamentary Private Secretary to Deputy Prime Minister of the United Kingdom, Nick Clegg.

Lamb stood at the subsequent Lib Dem leadership election, where he lost to Tim Farron on 16 July.

[11] On 24 October 2019 Lamb resigned from the group, writing to its secretariat "I do believe fundamentally in transparency and accountability to the public who ask questions.

[16] In his role as chair of the Science and Technology Committee, Lamb initiated measures that led to a significant improvement in medical research transparency in the UK.

Their son Archie Lamb was a co-founder of the independent record label Takeover Entertainment which promoted Tinchy Stryder.