Haley, 45, is the first ever Indian-American appointed to a Cabinet-level position by any president.
Haley, the former governor of SC, was a critic of Trump's during the 2016 Republican primaries and endorsed his opponent Sen.
Nikki Haley is the latest in a long list of senior staff members to leave the Trump administration.
Trump told reporters that he is hopeful that Haley will return to the administration at some point, perhaps in a different capacity.
Haley "has done an outstanding job" in her role as ambassador, fellow South Carolinian Lindsey Graham said.
Haley, in turn, called her tenure at the United Nations "the honor of a lifetime", saying, "I have been such a lucky girl to lead the state that raised me, and serve the country I love so much". "We've solved a lot of problems and we're in the process of solving a lot of problems", Trump said.
Tuesday's announcement prompted widespread praise of Haley's tenure from fellow Republicans, but some lawmakers expressed concerns about the timing.
The meeting will be covered by a White House pool reporter.
Congressional and Trump administration officials told the AP that Haley plans to resign.
The move comes as a surprise and a few weeks following the United Nations General Assembly where Haley was front and center as a representative of the Trump administration and the United States. She was quick to voice her own opinions on the big policy issues that are high on her agenda, like Iran and North Korea. She also often sides even more strongly with Israel than Trump, who has pushed USA policy away from its officially neutral stance on the conflict with the Palestinians.
There was also speculation that she may have been the author of the anonymous op-ed in the New York Times excoriating Trump - despite the fact that she had denied authorship and had written in support of Trump - the guesswork based on the fact that she was once a never-Trumper and had backed his rival Marco Rubio in the Presidential election campaign.
"I want to make sure this administration, this president, has the strongest person to fight", she said.
She's helped rein in Iranian aggression, moved progress on a denuclearized North Korea, assured Israel we have her back, and overall just gained the USA more respect on the global stage. "She knows everybody on a very first name basis and they like her, except for maybe a couple, which is normal".
Trump and Haley held a quickly arranged media availability Tuesday morning in the White House, shortly after Axios's Jonathan Swan broke the news of her impending exit. "It's not diplomatic, and they find it amusing".
"There's no personal reason", she said, explaining her rationale for departing.
Nikki Haley has been one of the most vocal and pro-active advocates for Israel in the United Nations the Jewish State has ever had.
UN envoy Nikki Haley and Israeli Ambassador to the UN Danny Danon on the Lebanese border, June 8, 2017. At the same time, Haley lost on key policy debates, including a further reduction in the number of refugees who can be resettled in the United States.