The 1941 Dunbartonshire by-election was held on 27 February 1941. The by-election was held due to the appointment as sheriff substitute of the incumbent Labour MP, Thomas Cassells. It was won by the Labour candidate Adam McKinlay.^[1]

Because of the wartime truce his only opponent was a Communist, who had a relatively strong vote, although the constituency did include the Vale of Leven, a "little Moscow". It took place before the Soviet Union entered the war when the Soviet Communist Party changed its line.