Gordon Brown will not face a vote if he is the only candidate to succeed Tony Blair as Labour leader, the party's National Executive Committee has said.
The chancellor is the favourite to succeed Mr Blair
But the chancellor will still have to attend hustings during a deputy election campaign due to last at least seven weeks, the NEC confirmed.
He is the favourite to succeed Mr Blair who has said he will go by September.
Two other MPs, left-wingers Michael Meacher and John McDonnell, have said they will run against him.
But they must first get the signatures of 44 other Labour MPs to get on to the ballot.
Mr McDonnell said: "I welcome the announcement of the timetable, as Labour Party members and affiliates all around the country are desperately keen to have a proper leadership election with a choice of candidates and a choice of policies."
Tuesday's decision, during a day-long meeting of the NEC at Westminster, spares Mr Brown having to go through an "affirmative ballot" if he is the only candidate.
Six MPs have confirmed they will run for the deputy leader's job, to replace John Prescott, who has said he will stand down with Mr Blair.
The contenders include five ministers - Peter Hain, Hilary Benn, Harriet Harman, Hazel Blears, Alan Johnson - and one backbencher, Jon Cruddas.
Mr Blair is expected to announce his retirement within days of the Scottish and Welsh elections on 3 May. It could mean Britain has a new prime minister as early as 22 June.
NEC general secretary Peter Watt said the executive would meet within 72 hours of an announcement to agree a timetable for the election.
Nominations would begin immediately afterwards, with MPs given three days on which the Commons is sitting to submit papers.
Hustings would be held over about six weeks - three in England, one in Scotland and one in Wales.
The ballots will go out about five weeks into the process and should take about two and a half weeks.
The winner of both the leadership and deputy leadership contest will have to secure more than 50% of the electoral college - under which party members, unions and MPs each have a third of the votes.
The NEC also confirmed that all new members would have a vote, waiving the usual qualifying period.
Labour chief whip Jacqui Smith said the rules would reflect the fact that, as well as choosing a new leader, the party was electing a prime minister for the first time.
"We will be electing both the leader and deputy leader but also the prime minister of this country and that is why we have been clear ... that we will expect the candidates to get out and talk to the Labour Party and to talk to the country," she told Sky News.