The Ashfield by-election was held on 28 April 1977 in the Ashfield constituency in the coal mining area of Nottinghamshire, following the resignation of Labour Member of Parliament David Marquand. Conservative candidate Tim Smith was the narrow winner in what was thought to have been a very safe Labour seat.
Marquand had resigned to take up a post at the European Commission in Brussels, as an advisor to the United Kingdom's newly appointed Commissioner Roy Jenkins. His majority at the October 1974 general election had been 22,915, which made the seat look very safe.
There was another by-election held on the same day, in Tony Crosland's nearby former seat of Grimsby which looked much more marginal. Crosland had died on 19 February 1977. The Labour Party directed most of its campaign effort into saving Grimsby, believing Ashfield was in no danger. This strategy succeeded in saving Grimsby, but allowed Tim Smith to win by 264 votes (after a recount) over Labour's Michael Cowan.
Smith was unable to hold the seat at the 1979 general election, when Labour's Frank Haynes won with a majority of 7,797.