Leonard Lloyd Duvall OBE is a British Labour and Co-operative politician who has been deputy chair of the London Assembly since May 2024. Additionally, Duvall has been serving as the Leader of the Labour Group in the London Assembly since 2004, and has been the Member of the London Assembly (AM) for Greenwich and Lewisham since 2000. Duvall is a former chair of both the Metropolitan Police Authority and the London Labour Party Regional Board.

The London Assembly is a 25-member elected body, part of the Greater London Authority, that scrutinises the activities of the Mayor of London and has the power, with a two-thirds supermajority, to amend the Mayor's annual budget and to reject the Mayor's draft statutory strategies. The London Assembly was established in 2000. It is also able to investigate other issues of importance to Londoners, publish its findings and recommendations, and make proposals to the Mayor.