Len McCluskey has announced he will step down next April as leader of the UK's biggest trade union Unite, but stand immediately for re-election.
The decision means he will step down a year early, but if re-elected he could be in post for a further five years until 2022.
Mr McCluskey said he wanted a show of support from Unite members to vindicate his leadership of the union.
He said: "I intend to submit my record to the vote of Unite members."
Unite's executive council has agreed that his resignation will take effect from 28 April, when the elections for general secretary and the executive council finish.
Mr McCluskey said: "I will remain general secretary until then - after that it is in the hands of the membership."
Unite said the decision would save money: "This will ensure the ballot for executive council members and the ballot for general secretary are conducted simultaneously, minimising the enormous costs caused to the union by the legal requirement to conduct the ballot by post and not by modern voting methods, thereby saving the union in the region of £1m," the union said.
"Following a period of candidate nominations, the ballot for both elections will commence on 27 March 2017, concluding on 28 April 2017."
Mr McCluskey has been the leader of Unite's 1.4 million members since he was first elected in 2010.
His plan could also influence the future of the Labour Party, where he has been a leading supporter of its leader, Jeremy Corbyn, and his anti-austerity politics.
Unite is Labour's biggest doner and provided Mr Corbyn's leadership campaign with cash, manpower and office space for phone bank volunteers.
Analysis: John Moylan, BBC industry correspondent
Len McCluskey's move is a gamble.
He has been a strong supporter of Jeremy Corbyn but some within this industrial union have been concerned by Mr Corbyn's plans to ban fracking, and also by his lukewarm support for new nuclear power.
His equivocal position on renewing the nuclear deterent Trident - as a lifelong anti-nuclear weapons campaigner - has also troubled many who work in the defence sector.
Unite says holding the election for general secretary a year early, at the same time as its internal executive council elections, will save the union up to £1m.
But with turnouts in union leader elections traditionally very low, Mr McCluskey's future now hangs on whether union activists will back him for a third time.