Francois Hollande officially became France's first Socialist president in 17 years as outgoing president Nicolas Sarkozy left the Elysee Palace for the last time.
Hollande walked up the red carpet at the start of the ceremony as the self-styled Mr Normal, but finished it as the seventh president of France's Fifth Republic.
Sarkozy handed over the levers of power including the country's nuclear codes and other secret dossiers, before bidding his successor goodbye on the steps of the Palace and leaving with his wife Carla Bruni-Sarkozy.
The official results of the presidential election were read out before Hollande was presented with the gold chain of the Legion d'Honneur, France's highest order of merit, by French army General Jean-Louis Georgelin.
Hollande is due to dash to Berlin later in the day to meet German Chancellor Angela Merkel -evidence of the priorities of a man who is dealing with renewed fears in the euro zone about a messy Greek exit from the single currency.
In his inaugural speech to some 400 guests, Hollande said he would seek to amend a European pact to add growth-boosting measures to deficit-cutting policies that critics say are dampening the bloc's growth prospects.
"To overcome the current crisis, Europe needs a project, needs solidarity, needs growth. I will propose a new pact to our partners which will ally the reduction of public debt, which is necessary, with an economic stimulus which is essential," he said.
Hollande wanted the event to be less lavish than it has been on previous occasions, reflecting his image as France's scooter-riding "Mr Normal" in contrast to his showman predecessor, dubbed "President Bling Bling" by some commentators.
Some three dozen or so of Hollande's personal guests joined officials at the Elysee, and Hollande has announced that his official car will be a hybrid Citroen.
But the somber tone of the occasion was hard to avoid. The gold medal presented to Hollande during the ceremony bears the names of all the previous presidents of the Fifth Republic, and he mentioned them all by name in his address. He is, however, the only Socialist apart from Francois Mitterrand ever to hold the office.