The by-election is the first since the general election Polls have closed in the Oldham East and Saddleworth by-election, the first such contest since the coalition government was formed last year.
The by-election was called after a specially convened election court found Labour Party candidate Phil Woolas had lied about his Lib Dem opponent.
Labour won the seat by just 103 votes in May from the Liberal Democrats with the Conservatives in third place.
The result is expected to be declared at about 0200 GMT on Friday.
The by-election is the first significant opportunity that voters have had to pass judgement on the policies of the coalition government and Ed Miliband’s performance as opposition leader.
All the main party leaders visited the constituency during the campaign, with Lib Dem leader Nick Clegg making three appearances to support his party’s candidate.
Polls have suggested Labour are on course to hold the seat.
However, BBC chief political correspondent Laura Kuenssberg said the indications were that the result would be close and that Labour were not taking victory for granted.
Labour sources have told the BBC they believe turnout in the contest was considerably lower than in the general election.
Between 40% and 45% of registered voters are thought to have cast their ballots before polls closed at 2200 GMT, compared with 61% in May.
Ten candidates are standing in the contest.
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