Unite leader Len McCluskey is stepping down and will seek re-election for a further term of office from next April, the union has announced.
Unite said Mr McCluskey decided to seek re-election as general secretary of the union after they announced that the ballot for Executive Council (EC) members and the ballot for leader are to be conducted at the same time in a bid to save them £1 million.
Mr McCluskey's current five-year term is due to end in 2018, so he is effectively bringing the election forward by a year.
The 66-year-old said: "I intend to be a candidate in the upcoming general secretary election and to submit my record to the vote of Unite members.
"This will be an election in which Unite will be under unprecedented scrutiny, particularly from our enemies. It is vital that in this period there is no lack of continuity in service or support to our membership, and that the full integrity of our procedures is not only protected, but seen to be protected."
Balloting will start in March and end on April 28, with assistant general secretary, Gail Cartmail, taking over as acting leader for the election period, a move Mr McCluskey said would ensure "that, while I am a candidate for re-election, the business of Unite remains properly managed".
The timetable was agreed by Unite's executive on Tuesday.