Macron, a 39-year-old centrist, took the reins of power from Socialist Francois Hollande at the Elysee Palace a week after his resounding victory over far-right leader Marine Le Pen in an election that was watched worldwide.
After a private meeting with his former mentor Hollande and his first speech as president, Macron headed up the rainy Champs Elysees in an army vehicle, waving to small crowds of well-wishers who gathered along the famed avenue.
Macron said his first priority would be "to give back to the French people the confidence that for too long has been flagging", while the second would be making France a beacon for democracy and freedom worldwide.
France's place was in the European Union "which protects us and enables us to project our values in the world," but he said the 28-member bloc needed to be "reformed and relaunched."
Macron also suggested he would press on with his ambitious but controversial agenda to reform France's rigid labour market and modernise the social security system despite the fierce resistance he is likely to meet.
"I will not reverse course on any of the commitments taken in front of the French people," he said, adding that "France is strong only if she is prosperous."
Some analysts and opponents have questioned the strength of Macron's mandate after he won just 24.01 per cent in the first round of the presidential election on 23 April before his landslide victory over Le Pen in the second. His opponents on the far-right and far-left, opposed to the EU and major economic reforms, won around 50 per cent of the first-round vote.
The former investment banker was proclaimed president by Laurent Fabius, president of the Constitutional Council, at the 18th-century presidential palace in central Paris where Macron and his wife Brigitte will now live. Brigitte, a 64-year-old who was his high school drama teacher, attended the ceremony wearing a light blue Louis Vuitton outfit.
Her three children were also present along with VIPs from France's political scene and the young team of close advisors behind Macron's sensational rise.
One early political backer, the mayor of the central city of Lyon, Gerard Collomb, wept as Macron greeted him. "In order to be the man of one's country, one must be the man of your time," Fabius told him, quoting the Romantic-era French writer Chateaubriand.
"You are now the man of your time and by the sovereign choice of the people, you are now, above all, the man of our country."
At the end of the formalities, a 21-gun salute rang out from the Invalides military hospital on the other side of the River Seine. The new president faces a host of daunting challenges including tackling stubbornly high unemployment, fighting Islamist-inspired violence and healing divisions exposed by an often vicious election campaign.
Hollande's five years in power were plagued by a sluggish economy and bloody terror attacks that killed more than 230 people and he leaves office after a single term. Security was tight around Paris, with around 1,500 police officers deployed near the presidential palace and on the Champs Elysees, and surrounding roads blocked off. Macron's first week will be busy.
On Monday, he is expected to reveal the closely-guarded name of his prime minister, before flying to Berlin to meet German Chancellor Angela Merkel. It is virtually a rite of passage for French leaders to make their first European trip to meet the leader of the other half of the so-called "motor" of the EU.
Pro-EU Macron wants to push for closer cooperation to help the bloc overcome the imminent departure of Britain, another of its most powerful members. He intends to press for the creation of a parliament and budget for the eurozone.
Merkel welcomed Macron's decisive 32-point victory over Le Pen, saying he carried "the hopes of millions of French people and also many in Germany and across Europe". Further ahead in June, Macron will need to win a majority in parliamentary elections to enact his ambitious reform agenda.