"Early this morning, the Government of Turkey ... said that they would be stopping combat and their offensive in Syria, making the ceasefire permanent, and it will indeed be permanent," Trump said in a formal statement from the White House.
Trump said sanctions the U.S. imposed on Turkey would be lifted "unless something happens that we're not happy with."
"Today’s announcement validates our course of action," he said, saying it had been scorned. "Now, people are saying: 'Wow, what a great outcome.'"
He claimed that the ceasefire is the sole outcome of his administration's efforts. Trump's announcement, though, came a day after Russian President Vladimir Putin and Turkish President Recep Tayyip Erdogan announced they had reached a separate deal for control of northeastern Syria -- where U.S forces have been withdrawn.
"This was an outcome created by us, the United States, and nobody else," Trump said. "No other nation, very simple. We're willing to take blame and we're also willing to take credit."
“We have done them a great service and we've done a great job for all of them," he said, speaking of the U.S.-allied Syrian Kurds and Syrian civilians caught in the crossfire. "And now we're getting out. A long time. We were supposed to be there for 30 days. That was almost 10 years ago,” he said, noting what he said was his promise to get the U.S. out of long-standing wars.
Turkey and Syria have been fighting for centuries, Trump said, adding, "Let someone else fight over this long-bloodstained sand. We've done a great job and now we're getting out."
The president also said he had spoken with the commander of the Syrian Kurdish forces who Trump claimed “could not have been more thankful” and that he assured Trump that “ISIS is under very, very strict lock and key, and the detention facilities are being strongly maintained.”
The president’s claim that the Syrian Kurds are “happy” with the U.S. withdrawal seemed to be contradicted by images of some Kurds throwing rotten vegetables at withdrawing U.S. troops,
Ahmed Omar, the president of the Syrian Democratic Council, said Monday that the Kurds have been “saddened” by the withdrawal and what he said was the slaughter of his people by Turkish forces: “They [Turks] said they want to kill hundreds of thousands of us ...This is why I ask President Trump to stop the attacks ... Help us to reach a political solution. We want peace. We are peaceful people.”
Just after touting success on Wednesday, though, the president seemed to doubt his own assessment saying permanent is "questionable" in that region.
"However, you would also define the word permanent and that part of the world is somewhat questionable," Trump said.
Even as Trump made his announcement, the top U.S. envoy for Syria, Amb. James Jeffrey, was testifying on Capitol Hill and seemed to contradict the president's assessment of success.
"The Turkish incursion into northeast Syria is a tragedy, it was long-standing U.S. government policy in two administrations to keep that from happening and we were clearly not successful."
The president first teased the announcement on Twitter Wednesday morning.
In his tweet, the president touted “big success” on the Turkish-Syria border, heralding that a safe zone has been created and that the ceasefire has held.
"Big success on the Turkey/Syria Border. Safe Zone created! Ceasefire has held and combat missions have ended. Kurds are safe and have worked very nicely with us. Captured ISIS prisoners secured. I will be making a statement at 11:00 A.M. from the White House. Thank you!" Trump tweeted.
The president's tweet comes a day after Russian President Vladimir Putin and Turkish President Recep Tayyip Erdogan announced they had reached a separate deal on how to divide up and control northeastern Syria -- from which U.S. forces recently withdrew.
The deal came just before the U.S.-Turkish halt in hostilities reached its deadline, with a senior Trump administration official touting it as "one of the best ceasefires I've ever seen."
But as the remaining 1,000 U.S. troops withdraw from northeast Syria at President Trump's command, critics have blasted Trump and his administration for ceding this territory to Turkey, Russia and Syrian President Bashar al-Assad, who has overseen a brutal war against his own people, and giving up leverage to accomplish U.S. goals in the region, including ensuring the defeat of the Islamic State and expelling Iranian forces from Syria that threaten U.S. allies, especially Israel.
The deal between Erdogan and Putin calls for Syrian Kurdish forces and their weapons to be removed from a buffer zone the length of the border in northeastern Syria -- an expansive area where these forces live now that extends 30 kilometers (18.6 miles) in from the border. Turkey would maintain control of the portion it now has, thanks to its agreement with the U.S., while Assad's forces, backed by Russia, would secure the rest of it.
ABC News' Conor Finnegan contributed to this report.