Lammy was born in Tottenham, a working-class area of North London, and brought up by his mother after his father left the family. He won an Inner London Education Authority choral scholarship to The King's School, Peterborough and studied for a degree in law at the School of Oriental and African Studies in London, and then took a Masters degree at Harvard Law School, the first black Briton to do so.
Lammy has commented on the UK's history of slavery, both in his role as Culture Minister to mark the 200th anniversary of the end of the slave trade in Britain and because he suspects there were slaves amongst his ancestors.
In 2000, he was elected as a Labour candidate on the London-wide list to the London Assembly. However, the sitting Member of Parliament for Tottenham Bernie Grant died during the campaign, and Lammy was selected to succeed him. He retained the seat, on a low turnout, in a by-election held on June 22, 2000, becoming the Baby of the House (the youngest MP). He was promoted to the government in 2002 and served at the Department for Constitutional Affairs from 2003 to 2005. Following the 2005 General Election, Lammy was appointed Minister for Culture under Tessa Jowell at the Department of Culture, Media and Sport.
Lammy has stated in speeches and articles that his vision for the arts in the UK is to move towards participation for all. In February 2006 he criticised the Arts Council of England leading to a conflict with its chairman.
On 29 June 2007 he was moved from Culture, Media and Sport to become a Parliamentary Under-Secretary of State in the newly created Department for Innovation, Universities and Skills, working under Secretary of State John Denham. In October 2008 he was promoted to Minister of State and it was announced he would be appointed to the Privy Council.
On general election night in 2005 he controversially dubbed George Galloway MP, of the Respect party, a "carpetbagger", and said he had "come down from Scotland to whip up racial tensions". Galloway contested that his prior constituency in Scotland was dissolved and that he had a right to stand as a British MP wherever he had support. Underlying the argument was Britain’s involvement in the Iraq war, of which Lammy was a vocal supporter, and its impact on community relations, which was a key issue for Galloway's Respect party.