Emmanuel Macron took his first steps as France's president-elect on Monday, but faces a tough task establishing a team that can govern effectively.
His party has announced it is changing name from En Marche to La Republique En Marche (Republic on the Move).
It must pick candidates quickly ahead of parliamentary elections on 11 and 18 June. It wants to be the biggest party but at the moment has no seats at all.
Mr Macron beat the far right's Marine Le Pen by 66.1 percent to 33.9 percent on Sunday.
But a low turnout and a record number of spoiled or blank votes showed disillusionment among many, particularly on the far left, at the choice they were given.
In a speech to jubilant supporters, Mr Macron said: "Tonight you won, France won. Everyone told us it was impossible, but they don't know France."
His win makes him France's youngest president and overturns the decades-long dominance of France's two main political parties.
But huge challenges remain, with a third of those who voted choosing Ms Le Pen, 48, and even more abstaining or casting a blank ballot.
Mr Macron said he had heard "the rage, anxiety and doubt that a lot of you have expressed", vowing to spend his five years in office "fighting the forces of division that undermine France".
He will be sworn in on Sunday, outgoing President François Hollande said.
Ms Le Pen has also signalled there will be a change to her National Front party. There are suggestions from its officials, too, that it will change its name. But she has vowed to lead the "new force" into the parliamentary elections.
Emmanuel Macron's first day as President-elect
Mr Macron inherits one of the most powerful positions in Europe, and all the symbolism that comes with it.
This morning at the Arc de Triomphe, he showed no sign of being awed by his new job.
He walked alongside the outgoing President François Hollande as the two laid a wreath at the Tomb of the Unknown Soldier.
The two then shook hands with veterans. Mr Macron appeared to take longer to make his way through one receiving line, stopping to talk to elderly men, leaving Mr Hollande to wait for him at the end.
Mr Macron now becomes France's youngest leader since Napoleon Bonaparte, whose battles are commemorated at the Arc de Triomphe. The new president will hope that his own fights are less bloody.