“An ally must be dependable,” said Mr Macron, who reportedly called Mr Trump to warn him against the plan.
The US said the Islamic State (IS) group had been defeated, a claim disputed by allies and US politicians.
France, a key part of the US-led coalition against IS in Syria and Iraq, said its troops would remain in Syria.
Some 2,000 US troops have helped rid much of Syria’s north-east of the jihadist group, but pockets of fighters remain.
Critics of Mr Trump’s decision say it could lead to a resurgence of the group, and Defence Secretary Jim Mattis resigned over the issue.
What has Mr Macron said?
Speaking on a visit to French troops in Chad, Mr Macron said: “To be allies is to fight shoulder to shoulder. It’s the most important thing for a head of state and head of the military.”
Mr Trump’s sudden announcement on Wednesday and Gen Mattis’ resignation sparked concern even among Republican supporters of the president.
The US special presidential envoy for the Global Coalition to Defeat IS, Brett McGurk, also quit over the decision.
Meanwhile, the French president paid tribute to Gen Mattis, calling him a “reliable partner”.