Michael Howard is to stand down after the Tories' October conference, paving the way for a new leader by Christmas.
Howard: Will stand down within months
Prior to the conference a convention is expected to decide on changes to the way the party chooses its leaders.
Mr Howard, 63, told the Daily Telegraph he wanted an "open and honest debate" about the future of the party and hoped to see a new leader by the end of 2005.
Most of Mr Howard's possible successors were given senior shadow cabinet jobs in a reshuffle on Tuesday.
One of the youngest MPs, 33-year-old George Osborne, was made shadow chancellor.
Former Foreign Secretary Sir Malcolm Rifkind, back in the Commons after eight years, also has a front bench job shadowing David Blunkett at the Department for Work and Pensions.
Liam Fox, who was party co-chairman, becomes shadow foreign secretary. Francis Maude becomes party chairman and David Cameron, 38, takes on education.
Former Tory deputy prime minister Michael Heseltine told BBC News: "I think it's a very dramatic re-shuffle. It's putting all the talent in the front line. It makes a nonsense of the suggestion that Michael [Howard] should go."
Mr Howard announced his plans to stand down after last week's general election defeat.
He said he would be too old to contest another election as leader, a decision which led Tory donor Lord Kalms to brand him a "lame duck".
The current Tory leadership selection system, means MPs narrow the choice to two candidates and party members have the final say.
Former leader William Hague, who introduced the system, says it should change so MPs make the final choice.
He backed Mr Howard's handover timetable, telling BBC News: "It does give the party time to reflect and to view the alternative candidates."
Mr Hague said he would not be a candidate for the leadership, however many people asked him, nor had he decided which contender he would support.
'Work to be done'
Mr Osborne will be staring across the Despatch Box at Gordon Brown, who in his eight years as chancellor has already seen off Tory hopefuls including Oliver Letwin, Mr Howard, Michael Portillo and Mr Maude.
Shadow chancellor - George Osborne
Shadow chief secretary to the Treasury - Philip Hammond
Shadow foreign secretary - Liam Fox
Education - David Cameron
Work and pensions - Sir Malcolm Rifkind
Defence - Michael Ancram
Shadow home secretary - David Davis
Rural affairs - Oliver Letwin
Northern Ireland - David Lidington
Chief whip - David Maclean
Family - Theresa May
Health - Andrew Lansley
Constitutional affairs - Oliver Heald
Transport - Alan Duncan
Shadow Commons leader - Chris Grayling
International development - Andrew Mitchell
Deregulation - John Redwood
Local and devolved government - Caroline Spelman
Oxford-educated Mr Osborne said he wanted to help broaden the appeal of the Conservative party through his economic policies.
He said there was nothing to do about his age, adding: "It is a great opportunity and I am going to take it on and bash Brown at the despatch box," he said.
David Davis, the bookmakers' favourite to be the next leader, remains shadow home secretary.
Former shadow chancellor Oliver Letwin said he had asked to be effectively demoted to the environment, food and rural affairs portfolio.
He said he had had his say on economic questions. His new role was of huge importance in his constituency and he thought the Tories could develop a distinctive view on the environment, he said.
There have been reports that Mr Letwin wants to return to being a director of merchant bank NM Rothchild but he said he did not know whether he would do other things.