Hollande beat Sarkozy, the conservative incumbent, in Sunday's runoff election to become the country's first Socialist president in 17 years, putting an end to a bruising election campaign.
In a ceremony at Paris' Arc de Triomphe, however, the two men stood side by side in silence laying a wreath at the Tomb of the Unknown Soldier to commemorate Victory in Europe Day and the surrender of Nazi forces on May 8, 1945.
The ceremony took place just days after voters in Greece, battered by years of austerity, voted an extreme-right party into parliament in a general election for the first time since the end of a military dictatorship in 1974.
"The French have voted and both presidents ... had to be here to pay homage to all those who laid down their lives for the country," Hollande told reporters.
"We faced each other in an election but it was our duty to be here at this ceremony. France's citizens should feel proud that the Republic is united," he said.
Hollande, the self-styled "Mr Normal,” sought throughout his campaign to brand himself as a man capable of uniting France after what his supporters said was a divisive five-year term by Sarkozy.
After a campaign dominated by anger over the economic crisis and Sarkozy's unpopular presidential style and perceived pandering to the rich, Hollande swept to victory on Sunday vowing to fight for equality and justice.
Hundreds of people took advantage of the public holiday and turned up at the Arc de Triomphe to watch the ceremony and pay their respects to Sarkozy in one of his last official acts.
Some held up banners saying "Thank You Sarkozy,” others shouted words of support for the conservative, who has said he might quit politics in the wake of his defeat.
"He did a lot for France. It's easy to make promises to please everybody but France is in crisis and he had the courage to stand up and say what everyone was thinking," a spectator called Angelique said, speaking of Sarkozy.
Hollande will be sworn in as president on May 15. His post-victory honeymoon is expected to be short-lived, with financial markets eager for clear signals on his policies and how hard he plans to push back German-led austerity.
His inauguration ceremony will be followed by a trip to Berlin next week, on May 16 or 17, to discuss incorporating pro-growth clauses into the European fiscal compact with German Chancellor Angela Merkel.
Merkel had publicly backed Sarkozy's campaign, and, in a sign of the tough negotiations Hollande faces, the German chancellor on Monday rejected the notion that Europe was on the brink of a policy shift. Her close allies have said they expect Hollande to have to make the lion's share of the concessions.
