A bill which would end the right of prime ministers to decide the date of the next general election is being brought forward by the Lib Dems.
Party leader Sir Menzies Campbell said they would be calling for fixed, four-year terms for governments.
Allowing hype to build about an early election was a "massive error of judgment" by Gordon Brown, he said.
As long as the decision rested with the PM, it would inevitably be influenced by "what's best for him", he added.
On Saturday the prime minister announced he would not be calling an early election - following weeks of speculation.
Sir Menzies said Mr Brown should not have allowed expectations to be "ramped up" by the Labour Party - adding: "It's going to hang round his neck for a very long time."
He said Lib Dem MPs David Heath and David Howarth would table a bill in the House of Commons on Monday that would see Parliamentary terms fixed at four years - which would make the next general election May 7, 2009.
He told the BBC: "It's high time, in my view, that the decision about a general election is not part of the discretion of the prime minister.
"Inevitably in those circumstances the prime minister's attitude will be conditioned by what he thinks is best for him and best for his party.
"We should have it done on a fixed full-term basis then everyone knows where they stand, the public has a degree of certainty and a degree of confidence in the process which the events of the last week have shown, is sadly lacking."
Conservative leader David Cameron has said there are "real drawbacks" to a fixed-term system but that it would be examined by the Tories.
Earlier Lib Dem president Simon Hughes said the party had been expecting to win seats from the Conservatives and Labour in an autumn general election.
He told the BBC's Andrew Marr pregramme: "We were ready for an election, we believed we would do well in an election."
Mr Hughes also rejected the suggestion the Lib Dems might now want to replace Sir Menzies, 66, as leader.
"The only criticism that was ever made was that you couldn't have a party leader who was of a certain age, and Ming addressed that head on in the conference," Mr Hughes said.
"He made the point that when it comes to crucial decisions it is the experience that counts.
"We would not have had Menzies Campbell making announcements about soldiers in Iraq, playing party games with soldiers in Iraq, saying that we were going to bring 1,000 home when he had already made half the announcement.
"So you have a leader with experience internationally and nationally and the party has chosen him for a fixed term and for the next election - whenever that is."
Mr Hughes denied opinion polls had been "atrocious" for the party and said when they were given equal media coverage - as they were during election campaigns - they did better in the polls.