The statement from Macron's former boss - Macron was economy minister when Valls was premier - shows how the political map is being re-drawn in France in the wake of the 39-year-old's crushing victory over far-right candidate Marine Le Pen on Sunday. The broader movement also has more opportunities to make gains with elections coming later this year in Germany, Norway, Denmark, the Czech Republic, and Portugal, among others. But first, he must choose a Prime Minister and win support from the deputies of the French Parliament, without which his Presidency could be largely unworkable. He was supported by 141 voters, while second Francois Fillon received 96 votes and third Le Pen 27 votes.
Marechal-Le Pen, whom some in the party hope will eventually take over from her aunt, and who always gets loud applause at party rallies, is more conservative on social and economic issues.
"The Socialist Party is dead; it's in the past", Valls said on Tuesday.
The losers of the presidential election are aiming to capitalise on a general lack of enthusiasm for the pro- business Macron - whom many voters backed exclusively to bar Le Pen - to bounce back in the parliamentary vote.
The centre-left Socialists and centre-right Republicans, both of which were trounced in the elections, are divided on whether they are willing to work with Macron, and the hard left remains implacably opposed to him.
The incoming president has said half of the candidates for the 577 seats up for grabs in the two-round June 11-18 elections to the National Assembly will be new to politics.
He won with some 66 per cent of the vote in the run-off election.
And if one party manages to steal a march on En Marche and seize a legislative majority, Macron will have to put up with whatever prime minister and legislation that party wants to pass - or risk losing his job to a no-confidence vote.
Sylvie Goulard, a French deputy to the European Parliament, said Macron would make Berlin his first official visit, with perhaps a stop to see French troops stationed overseas as well.
Now, however, Mr. Macron needs all his talents, and maybe more luck, to govern effectively.
Macron's victory has also led to much soul searching on the British centre-left. That is largely down to the fact that markets were virtually certain of a Macron victory, and had priced it in accordingly.
France's CAC 40 index, which last week touched the highest level since early 2008, slipped 1 per cent on Monday.