"I have ordered the French army to intervene tonight as part of the worldwide operation in coalition with the USA and Britain directed against the secret chemical arsenal of the Syrian regime", he said.
"Ten days ago, President Trump wanted to withdraw from Syria".
Appearing live on French television BFM and online investigative site Mediapart, the 40-year-old leader said the US, Britain and France had "full global legitimacy to intervene" with the strikes, to enforce worldwide humanitarian law.
"The U.S. mission has not changed - the President has been clear that he wants USA forces to come home as quickly as possible", press secretary Sarah Sanders said in a statement.
She added that Washington was "determined to completely crush" the Islamic State group in the country "and create the conditions that will prevent its return".
France said on Saturday it would not hesitate to strike Syrian government targets again if the chemical red line was crossed, but that no new strikes were planned at this stage, adding that it would renew a push for peace through dialogue with Russian Federation.
Macron said he hopes to bring Putin's Russian Federation and Erdogan's Turkey to the negotiating table in order to find a political solution for Syria.
But he also appeared anxious to avoid a wider conflict, saying France would "in no way allow an escalation". "The EU will stand with our allies on the side of justice", European Council President Donald Tusk tweeted.
Mr Macron described the alleged chemical weapons attack on April 7 in the Syrian city of Douma as being responsible for the "deaths of dozens of men, women and children".
The NATO alliance gave its full backing; NATO Secretary-General Jens Stoltenberg said the attack was about ensuring that chemical weapons can not be used with impunity.
The allied missile attacks in Syria were "legitimate", "limited" and "proportionate", French Foreign Minister Jean-Yves Le Drian said.
"We support the fact that our U.S., United Kingdom and French allies took on responsibility in this way as permanent members of the U.N. Security Council".
"Our allies had evidence that chemical weapons had been used, and we had proof that these weapons could be attributed to the Syrian regime, which led us to conduct this intervention", Macron added.
U.S. Ambassador to the U.N. Nikki Haley made clear the United States would not pull troops out of Syria right away, saying U.S. involvement there "is not done".
The leader detailed the success of the mission that saw France, the United Kingdom and U.S. rain terror down on Syria.
A day after France joined the United States and Britain in launching aggression on Syria, Macron insisted the intervention was "legitimate" and urged worldwide powers to push for a diplomatic solution to the seven-year war.