Macron, 39, was elected France's youngest-ever president on Sunday, crushing far-right leader Marine Le Pen after a bruising campaign that left France's traditional parties by the wayside.
He faces a huge task to unite a fractured, anxious country and to win a parliamentary majority in June's general election, without which he could struggle to implement his ambitious reform agenda.
Macron's victory at the head of a year-old movement that has presented itself as a home for progressives of all stripes has blown up France's long-standing left-right political divide.
Today, former Socialist prime minister Manuel Valls -- a failed candidate for his party's presidential nomination -- said he wanted to run for parliament on Macron's ticket.
"This Socialist Party is dead, it is behind us," said Valls, a reform-minded premier from 2014 to 2016 when Macron was economy minister.
"I will be a candidate for the presidential majority," the 54-year-old Valls told RTL radio, while insisting he remained a Socialist and "a man of the left".
Macron's "Republique en Marche" (Republic on the Move) movement, which has been keeping its distance from the political old guard, reacted warily to the announcement.
A spokesman for Macron's campaign said Valls "had a good chance" of being accepted into the fold but would have to submit an official application.
Socialist leader Jean-Christophe Cambadelis attempted to prevent a wave of defections to Macron's camp, warning Valls he could not remain a party member and run for parliament on Macron's ticket.
"That's impossible," he said.
A relative newcomer to politics, the europhile Macron swept to victory with 66.1 per cent of the vote on a tide of opposition to Le Pen's anti-immigration, anti-EU platform.
He has promised to liberalise the economy and rejuvenate France's jaded governing class by bringing more people who, like him, have never held elected office into government and parliament.