The stunning move will have extraordinary geopolitical ramifications and throws into question the fate of US-backed Kurdish fighters who have been tackling Islamic State miliants.
The US has reportedly begun informing partners in north-eastern Syria of their plans for an immediate pull out of troops, after a long campaign against the Islamic State.
"The Pentagon has an order to get to move troops out of Syria as quickly as possible," a US official said, according to the Wall Street Journal.
The US State Department is evacuating all of its personnel from Syria within 24 hours, a US official told Reuters.
US President Donald Trump on Wednesday tweeted: "We have defeated ISIS in Syria, my only reason for being there during the Trump Presidency."
Around 2,000 US troops have worked alongside Syrian militant groups, most notably Kurdish forces, to defeat the Islamic State in north-eastern Syria, but pockets of fighters remain.
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The surprise US move follows a call last week between Trump and Turkish President Recep Tayyip Erdogan, who had threatened to launch an "imminent assault" on Kurdish-controlled areas of northern Syria.
Turkey views the YPG as a terrorist group because of its links to the Kurdish insurgency within its territory, but the US has relied on Kurdish forces to help defeat the Islamic State group.
Following their conversation, Erdogan said that he had received "positive answers" from President Donald Trump on the situation in north-eastern Syria.
Trump has long expressed frustration about an open-ended Syria presence, while US military and state department officials have embraced a strategy of keeping troops in the country to defeat IS and act as a deterrent to Iran's expansionist ambitions.
Officially, US forces in Syria only have authority to defeat IS and ensure the group is unable to reform.
Trump's national security adviser John Bolton said in September, however, that US forces would remain in Syria until Iran withdraws its forces.
A total withdrawal of US troops in Syria would still leave a large military presence in the region, including more than 5,000 troops in neighbouring Iraq.
Israel's UN envoy Danny Danon said his country would respect any US decision but would continue to act against any Iranian presence in Syria which it deems threatening.
'Dream scenario' for Assad
IS swept across large swaths of Syria and neighboring Iraq in 2014, implementing their brutal interpretation of Islamic law in areas they controlled.
But they have since seen their dream of a state crumble, as they have lost most of that territory to various offensives.
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In Syria, IS fighters are holding out in what remains of the pocket that once included Hajin, including the villages of Al-Shaafa and Sousa.
The US military estimates that around 2,000 IS fighters remain in a small stretch of Syrian territory near the border with Iraq.
But earlier this year a Defence Department inspector put the number of IS members in Syria and Iraq as high as 30,000.
The decision to withdraw marks a shocking development not just for Kurds in Syria, but for long-established US doctrine in the region.
Only last week Brett McGurk, the special envoy to defeat IS, said: "nobody is declaring a mission accomplished."
"The military objective is the enduring defeat of ISIS. And if we've learned one thing over the years, enduring defeat of a group like this means you can't just defeat their physical space and then leave."
A US presence in Syria is seen as key to pushing against Iranian influence in the country and across the broader region. Tehran militias have supported the regime of President Bashar al-Assad.
Republican Senator Lindsey Graham, a Trump ally, said the president's decision was shortsighted.
"President @realDonaldTrump is right to want to contain Iranian expansion," Graham said on Twitter.
"However, withdrawal of our forces in Syria mightily undercuts that effort and put our allies, the Kurds at risk."
Charles Lister, a senior fellow at the Middle East Institute, called the decision "extraordinarily short-sighted and naive."
"This move will look like a 'withdrawal,' not a 'victory,' and yet more evidence of the dangerous unpredictability of the US president," Lister said.
"This is not just a dream scenario for ISIS, but also for Russia, Iran and the Assad regime, all of whom stand to benefit substantially from a US withdrawal."