The Glenrothes by-election will take place on 6 November, Labour MPs have been told.
It has not yet been decided if Prime Minister Gordon Brown will be campaigning ahead of the contest.
The seat, in Fife, has been vacant since the death of Labour MP John MacDougall in August.
The Labour Party is defending a 10,600 majority from the last general election, in 2005. The by-election writ could be moved on Tuesday.
The seat neighbours Mr Brown's Kirkcaldy and Cowdenbeath constituency.
Mr MacDougall, a former leader of Fife Council who was first elected to the Commons in 2001, was 60 when he died from mesothelioma.
Candidates picked
MPs were told of the selected by-election date at a meeting of the Parliamentary Labour Party on Monday.
Scottish Secretary Jim Murphy is expected to confirm it during a visit to Glenrothes on Tuesday.
Labour won the seat in 2005 with 19,395 votes, followed by the Scottish National Party on 8,731, the Liberal Democrats on 4,728 and the Conservatives on 2,651.
Labour has selected Lindsay Roy, the 59-year-old rector of Kirkcaldy High School, as its by-election candidate.
Peter Grant, leader of Fife Council, has been nominated by the party to contest the seat for the Scottish National Party.
The Conservatives have chosen 28-year-old Maurice Golden, 28, an environmental campaign manager for Keep Scotland Beautiful, while businessman Harry Wills will run for the Liberal Democrats.
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