The move marks Mr Obama’s first foray into international politics since leaving the White House in January.
Mr Macron released a video from Mr Obama on Thursday with the former president touting his candidacy.
“I have admired the campaign that Emmanuel Macron has run,” Mr Obama said.
“He has stood up for liberal values; he put forward a vision for the important role that France plays in Europe and around the world; and he is committed to a better future for the French people. He appeals to people’s hopes, and not their fears.”
Mr Macron is facing far-right candidate Marine Le Pen in Sunday’s run-off vote. Polls suggest Mr Macron is well ahead.
Mr Obama said he does not plan to get involved often in political situations.
“I’m not planning to get involved in many elections now that I don’t have to run for office again, but the French election is very important to the future of France and the values that we care so much about. Because the success of France matters to the entire world,” he said.
Mr Macron asked Mr Obama for his support, an Obama aide said.
Mr Obama ended his message with the words “En Marche,” the name of Mr Macron’s political movement which means “In Motion”, and “Vive La France”.
President Donald Trump has praised Mr Macron’s opponent, Ms Le Pen, although he has not explicitly endorsed her.
“She’s the strongest on borders, and she’s the strongest on what’s been going on in France,” Mr Trump said on April 21. “Whoever is the toughest on radical Islamic terrorism, and whoever is the toughest at the borders, will do well in the election.”
Meanwhile, allegations of fake news and hacking attempts dominated France’s presidential campaign on Thursday.
Paris prosecutors launched a preliminary investigation into whether fake news is being used to influence Sunday’s vote, as Mr Macron and Ms Le Pen rallied thousands at their last major campaign events.
There has been intense anxiety in France over the possibility that viral misinformation or hackers could influence the presidential vote, as in the US election last year. Those fears have largely failed to materialise.
Mr Macron’s campaign filed a lawsuit against an unknown source “X’’ after Ms Le Pen suggested during their only one-on-one debate that the former banker could have an offshore account.
“I hope we won’t find out you have an offshore account in the Bahamas,” Ms Le Pen said during the tense prime-time showdown on Wednesday night.
She appeared to be referring to two sets of apparent forgeries, published just hours earlier, that purported to show Mr Macron was somehow involved with a Caribbean bank and a firm based on the island of Nevis.
Mr Macron’s camp said the former investment banker was the victim of a “cyber-misinformation campaign”.
Speaking on France Inter radio, Mr Macron blamed Ms Le Pen for spreading “fake news” and said he never held a bank account “in any tax haven whatsoever”.
“All this is factually inaccurate,” Mr Macron said.
Later, Ms Le Pen’s campaign said a far-left hacker was arrested and had confessed to repeatedly targeting its website. In a statement, the campaign gave few details about the seriousness of the interference, which could range from attempts at defacing the website to flooding it with bogus traffic.
Police referred questions to prosecutors, who would not comment.
In a fiery speech delivered late on Thursday in a field in northern France, Ms Le Pen made an emotional appeal to desperate farmers, the jobless and the disillusioned.
Painting herself as the “voice of the people,” she said her rival would continue the painful status quo.
Thousands of supporters climbed on hay bales or clustered in the field in the village of Ennemain to hear her speak, chanting “We love you Marine!” and “Marine President!”
Ms Le Pen said she represents “the widow of the farmer who killed himself because he couldn’t stand it any more” as well as the company chief who sees a public bid go to a foreign competitor, and the taxi driver who lost his job to “Uberisation”.
Mr Macron, meanwhile, was on France’s southern edge in the Pyrenees town of Albi, visiting disgruntled workers at a glass factory before holding his last campaign rally in which he called on voters from the left and right to choose his reformist, pro-European platform.
He pledged to “give strength back to the country” and “build a more efficient and fair society”.