The 1939 Colne Valley by-election was a parliamentary by-election held on 27 July 1939 for the British House of Commons constituency of Colne Valley.

Ernest Marklew, who had been a Councillor in Grimsby, was first elected as MP for Colne Valley in 1935 when he gained the seat from the Liberal Party.^{[citation needed]} He died on 14 June 1939, forcing a by-election on the Labour Party.^{[citation needed]}

The Labour Party selected 52-year-old Glenvil Hall to defend the seat. He had been Labour MP for Portsmouth Central from 1929 to 1931.^{[citation needed]} The Liberal Party selected 34-year-old Lance Mallalieu to fight the seat. He had been the MP for the seat from 1931 until defeated by Marklew at the last General Election in 1935.^{[citation needed]} The Conservative Party selected 41-year-old Cecil Pike as their new candidate. He had been Conservative MP for Sheffield Attercliffe from 1931 to 1935.^{[citation needed]}

Hall continued as MP for Colne Valley until his death in 1962. He served as Financial Secretary to the Treasury in the 1945-50 Labour government.^{[citation needed]} Mallalieu left the Liberal Party for Labour before being elected Labour MP for Brigg in 1948.^{[citation needed]} Pike did not contest another election.^{[citation needed]}

• British Parliamentary Election Results 1918-1949, compiled and edited by F.W.S. Craig (The Macmillan Press 1979)