The Brigg by-election, 1948 was a by-election held on 24 March 1948 for the British House of Commons constituency of Brigg in Lincolnshire.
The by-election was triggered by the resignation of the constituency's Labour Party Member of Parliament (MP) Tom Williamson, a trade union leader who had held the seat since the 1945 general election.
The result was a victory for the Labour candidate Lance Mallalieu, who held the seat with a reduced majority, and represented Brigg until he retired from the House of Commons in 1974.