Greater Manchester Mayor Andy Burnham has announced that he intends to stand in the Gorton and Denton by-election, setting up a potential return to Westminster.
Mr Burnham said he had applied to the British Labour Party's National Executive Committee (NEC) for permission to seek selection for the contest.
He said the decision had been "difficult", but now was "the moment to mount the strongest possible defence of what we stand for".
Andrew Gwynne, the former MP for the Greater Manchester seat, formally quit yesterday, paving the way for a by-election to take place.
The NEC can still block his bid for selection by refusing permission, and supporters of party leader Keir Starmer are reported to be mobilising to prevent him from becoming a candidate.
But senior Labour figures have called for Mr Burnham to be allowed to stand, with the party's deputy leader, Lucy Powell, saying the decision should be up to local party members.
London Mayor Sir Sadiq Khan explicitly called for him to be allowed to contest the election, telling a centre-left conference in London: "I think if Andy Burnham wants to be a member of Parliament, Andy Burnham should be allowed to be a member of Parliament."
A selection process is expected to take place over the course of next week, ending with a hustings and NEC endorsement by Saturday 31 January.
