Gordon Brown will introduce fixed-term Parliaments if Labour is re-elected on May 6.
The Prime Minister said the move would be a manifesto commitment for his party at the General Election.
He also pledged a referendum on Lords reform and changes to electing MPs as part of what he called "the most comprehensive programme of constitutional reform for a century".
In a speech to Labour supporters in central London, the Prime Minister said he would also ban MPs from working for lobbying companies.
Voters would be given the power to recall MPs guilty of "gross financial misconduct" and there would also be a free vote in Parliament on giving people the vote at 16, he said.
Mr Brown added: "And in order to reassure people in this new century that the executive will no longer be able to determine when it should put itself forward for the people's approval, Labour's manifesto will include a new commitment to fixed-term parliaments."
