The 2007 Sedgefield by-election was a by-election held on 19 July 2007 for the House of Commons constituency of Sedgefield in County Durham. The Ealing Southall by-election was also held on 19 July. The by-election was triggered when Tony Blair, the Labour Party Member of Parliament (MP) for Sedgefield and former Prime Minister, resigned to become envoy for the international diplomatic Quartet on the Middle East. Blair accepted the office of Steward and Bailiff of the Three Hundreds of Chiltern, thereby disqualifying himself from Parliament and causing the by-election. Blair had held the constituency since its creation for the 1983 election, and Labour had held its predecessor constituencies since the 1935 election.