The 1943 Daventry by-election was a parliamentary by-election for the British House of Commons constituency of Daventry, Northamptonshire, on 20 April 1943.

The by-election was caused by the death of the sitting MP and Speaker, Edward FitzRoy on 3 March 1943. He had been MP here since winning the seat as a Conservative when the seat was created in 1918.

The result at the last general election was as follows:

The local Conservatives selected 38-year-old Reginald Manningham-Buller.^[2] The Labour party had selected Paul Williams.^[3] At the outbreak of war, the Conservative, Liberal and Labour parties had agreed an electoral truce which meant that when a by-election occurred, the party that was defending the seat would not be opposed by an official candidate from the other two parties. When the Labour and Liberal parties joined the Coalition government, it was agreed that any by-election candidate defending a government seat would receive a letter of endorsement jointly signed by all the party leaders.

Dennis Webb was Chairman of the Common Wealth party's Northampton branch.^[4] and came forward as a candidate. Liberal party member William Dyer decided to break the electoral truce and stand as an Independent Liberal.

Polling day was set for 20 April 1943, 48 days after the death of Fitzroy, allowing for a long campaign. When nominations closed, it was to reveal a three horse race.

Manningham-Buller received a joint letter of endorsement from all the leaders of the parties in the coalition.

Manningham-Buller addressing a campaign meeting said "Three countries will be pleased if I am defeated - Germany, Italy and Japan."^[5]

Paul Williams, who had been Labour's prospective candidate at the start of the war, ran Manningham-Buller close. Dyer, now standing officially as the Liberal party candidate. The result at the following General election;

• List of United Kingdom by-elections
• United Kingdom by-election records