Trump made the pledge during an extraordinary summit at the White House on Monday, where he hosted Zelenskiy and a group of European allies two days after Trump met with Russian President Vladimir Putin in Alaska and months after a disastrous Oval Office meeting where Trump and Vice President JD Vance publicly criticised the Ukrainian leader.
A peace deal appears far from imminent, however. Both Trump and Zelenskiy said they hoped the gathering would eventually lead to trilateral talks with Putin.
The Kremlin has not yet publicly accepted such a meeting, and it remains to be seen whether Putin, whose forces have been slowly grinding forward in eastern Ukraine, is prepared to sit down with Zelenskiy or make meaningful concessions.
Meanwhile, European leaders - who rushed to Washington in support of Ukraine - urged Trump to insist that Putin agree to a ceasefire before any talks can advance.
Trump had previously backed that proposal but reversed course after meeting with Putin on Friday, instead adopting Moscow's position that any peace agreement be comprehensive.
Trump told reporters in the Oval Office he liked the concept of a ceasefire but that the two sides could work on a peace deal while the fighting continued.
"I wish they could stop, I'd like them to stop," he said.
"But strategically that could be a disadvantage for one side or the other."
German Chancellor Friedrich Merz and French President Emmanuel Macron both voiced support for a ceasefire as a prerequisite to any direct talks with Russia.
"I can't imagine that the next meeting would take place without a ceasefire," said Merz, sitting at a table with Trump and other leaders.
"So let's work on that and let's try to put pressure on Russia."
Macron also said European leaders would need to be involved in subsequent meetings as well.
"When we speak about security guarantees, we speak about the whole security of the European continent," he told Trump.
Trump, who said repeatedly that he believes Putin wants to end the war, said he had spoken to Putin on Monday and would call him after the talks as well.
The Russian Foreign Ministry said on Monday that Moscow does not consider the deployment of NATO troops in Ukraine a viable solution to the conflict.
Trump and Zelenskiy's meeting was starkly different in tone from their previous Oval Office encounter in February, which ended when Trump and Vance publicly upbraided Zelenskiy as not being grateful enough.
This time, the meeting appeared far more convivial, despite the US president's movement toward Russia in recent days. Zelenskiy struck a deferential tone, giving thanks at least eight times during his opening remarks to the media.
Zelenskiy was also backed by the leaders of Britain, Germany, France, Italy, Finland, the European Union and NATO, who travelled to Washington to demonstrate solidarity with Ukraine and push for strong security guarantees for the country in any post-war settlement.
Trump greeted Zelenskiy warmly upon his arrival outside the White House, expressing admiration for Zelenskiy's black suit, a departure from his typical military clothes.
When a reporter asked Trump what his message was to the people of Ukraine, he said, "We love them". Zelenskiy thanked him, and Trump put his hand on Zelenskiy's back in a show of affection.
Following their one-on-one discussion, Trump and Zelenskiy held broader talks with the European leaders.
Zelenskiy described the private talks with Trump as "very good" and said they had spoken about Ukraine's need for US security guarantees.
"This is very important, that the United States gives such a strong signal and is ready for security guarantees," Zelenskiy said.
Trump said he and Zelenskiy had covered "a lot of territory" during their discussion.
"When it comes to security, there's going to be a lot of help," Trump said, adding that European countries would be involved.
"They are a first line of defence because they're there, but we'll help them out."
Trump's team has said there will have to be compromises on both sides to end the conflict. But the president himself has put the burden on Zelenskiy, saying Ukraine should give up hopes of getting back Crimea, annexed by Russia in 2014, or of joining the NATO military alliance.
Zelenskiy has already all but rejected the outline of Putin's proposals from the Alaska meeting. Those include handing over the remaining quarter of its eastern Donetsk region, which is largely controlled by Russia. Any concession of Ukrainian territory would have to be approved by a referendum.
