President Jacques Chirac had promised during the 2002 campaign to enact the two-pronged reform intended to clarify the legal status of the head of state after he was embroiled in controversy over a corruption probe.
The provisions adopted in a joint session of the National Assembly and the Senate confirmed that a sitting president is immune from prosecution but could be exposed to charges once he leaves office.
The amendment also gave parliament the authority to launch impeachment proceedings against a president for conduct incompatible with the exercise of his duties.
"By adopting this reform, I want every one of us to be aware that we are strengthening the Fifth Republic," Prime Minister Dominique de Villepin told members of the Congress, the two-chamber assembly, meeting in Versailles.
"We are bearing proof of its ability to evolve, to adapt to new circumstances and to the demands of our citizens," said Villepin.
The changes strike a balance between the need for transparency, the equality of all citizens before the law and the stability of the state, added the prime minister.
The amendment was adopted by a vote of 449 to 203, with 217 abstentions.
Under the changes, a two-thirds majority of votes from both houses is required to launch the impeachment proceedings against the president.
Chirac may face probe
The vote followed two landmark court rulings reached early in Chirac's mandate, which established that a serving president cannot be prosecuted, charged or forced to testify in a common law case.
The two rulings, by the Constitutional Court in 1999 and France's highest appeals court, the Cour de Cassation, in 2001, sparked controversy by enabling Chirac to avoid questioning in a corruption probe.
But they also specified that the president's time in office should not be taken into account under the statute of limitations, meaning Chirac could be questioned once he stands down.
In particular he could be investigated over illegal salaries paid to members of his party out of Paris municipal coffers between 1988 and 1995 -- over which his ally and former prime minister Alain Juppe was convicted in 2004.