Lammy was born in Tottenham, North London. He studied law at the School of Oriental and African Studies, University of London, obtaining a first-class degree. Lammy went onto study an LL.M. at Harvard Law School and is a member of Lincoln's Inn having been called to the Bar of England and Wales in 1994.
In 2000 he was elected for Labour for Tottenham, in a by-election held on 22 June 2000. In 2002 he became Parliamentary under-Secretary in the Department of Health. In 2003 Lammy was appointed as a Minister in the Department for Constitutional Affairs. After the 2005 general election Lammy was appointed Minister for Culture at the Department of Culture, Media and Sport. In June 2007 Lammy was appointed as a Parliamentary Under-Secretary of State in the Department for Innovation, Universities and Skills. In October 2008 he was promoted to Minister of State and was appointed to the Privy Council. In June 2009 the Department for Innovation, Universities and Skills was abolished and merged with the Department for Business, Enterprise and Regulatory Reform to form the Department for Business, Innovation and Skills. Lammy continued in the new department in his previous role as the Minister for Higher Education. After Labour lost the 2010 general election he turned down a post in the Shadow Cabinet and asserted a need to speak on a wide range of issues that would arise in his constituency due to the cuts in the public services that his constituents rely on.
In November 2011, he published a book – Out of the Ashes: Britain after the Riots – that serves as his account on the causes and consequences of the August 2011 riots.