Michael Howard has called on Tory activists to give the party's MPs the final say on choosing his successor.
Michael Howard said being a unified team was a main priority
The Conservative Party leader told its National Convention that whoever succeeds him must be confident they "command the clear support" of MPs.
Meanwhile, ex-Tory chairman Lord Patten has announced his support for his former cabinet colleague Kenneth Clarke in the party's leadership contest.
He said Mr Clarke was the public's favourite candidate.
Lord Patten also said he was the candidate Tony Blair would least like to win.
Mr Clarke later told the BBC he would find Gordon Brown "very defeatable" if the chancellor took over from Mr Blair.
Mr Howard made an unexpected appearance before the meeting in London, where members considered changes to the selection process.
He said the top priority for the party at every level was returning to government.
"One of the essential elements if we are to achieve that goal is a unified, disciplined parliamentary party," he said.
Mr Howard said being Leader of the Opposition was often considered "the toughest job in politics" and anyone doing it needed to know they could rely on a "united disciplined team".
Under the current system, MPs select two candidates and ordinary party members vote on them.
The planned changes would see party members asked to rate candidates who have the backing of 5% of MPs. The final decision would then go back to the parliamentary party.
Mr Howard announced he was quitting after losing the general election in May, but said he would give the party time to change the leadership election system before standing down.
Backing Mr Clarke to be next leader, Lord Patten said the former chancellor had "more experience than anybody else" and was "a wonderful combative House of Commons performer, who was right on Iraq".
Mr Patten said: "It would be nice if both the country and Parliament and MPs were sensible this time and they actually voted for a winner."
Later Mr Clarke told BBC Radio 4's Talking Politics show he was in the best position of the Conservative candidates to beat Mr Brown, due to his previous experience of being a "successful" chancellor.
"I can't think of anyone in a better position to get in and say 'Look, Gordon, you inherited a very good economy from me - look what you've done to it'."
Party chairman Francis Maude has warned grassroots members its electoral chances could be hit if proposals to change the way the leader is chosen are rejected.
However, several former chairmen have warned the changes could make the party less representative, as it would leave members from parts of the country without a Conservative MP without a say.
On Saturday, shadow trade and industry secretary David Willetts expressed concern about the proposed changes, saying Conservative Party members worked "tirelessly" for the organisation.
"Those members deserve a say in the leadership of the party they support, and any proposals that do not facilitate democratic involvement deserve to be defeated," he said.
"It is wrong to be trying to change the rules for electing the leader when a leadership contest is in practice under way," he added.
In 2001, the only time the existing rules were used, Iain Duncan Smith was elected leader over Mr Clarke.
The proposed new system will go to a vote at a convention of local branch chairman and other Tory figures.
It is also being considered by 1,300 senior party members in a ballot which closes on 27 September.
All the potential leadership candidates will have a chance to speak from the platform at the Conservatives' annual conference in Blackpool in early October.
If the changes are voted in, nominations for the contest would be likely to open the following week, with the new leader in place by mid-November.
If the changes are not backed, the existing system for choosing a leader will be used - which would mean a result would be expected in the New Year.
So far leadership hopefuls include former chancellor Mr Clarke, shadow education secretary David Cameron and former foreign secretary Sir Malcolm Rifkind.