"The success of France matters to the entire world," the former president said in a video posted online and tweeted by the Macron's campaign. The candidate "appeals to people's hopes and not their fears," Obama added.
Macron, an ex-investment banker, economy minister and advocate of a free market is up against Le Pen, who's running a strident "French-first," anti-globalization campaign.
The race is broadly seen as a litmus test for the strength of liberal values in the face of populist, economic protectionist movements such as Le Pen's National Front.
Obama added: "I know that you face many challenges and I want all my friends in France to know how much I am rooting for your success. Because of how important this election is I also want you to know that I am supporting Emmanuel Macron to lead you forward."
Le Pen's anti-immigrant and anti-Muslim message has found fertile ground in France, where Islamist militant attacks have killed more than 230 people over two years and plunged the country into a long-term state of emergency.
Macron, a former banker at Rothschild, has tried to counter her message by calling calling for France to focus on benefiting from globalization.
Voters head to the polls on Sunday.