Trump told reporters that Haley submitted her resignation to him six months ago, telling him that she needed to take a step back from politics after two years in office.
"More instability in an already unstable Trump administration", Rep.
Haley sought to tamp down speculation she may challenge President Trump in two years.
Haley told the president that her resignation would be effective in January 2019 to "give you time to select a replacement and to give the Senate time to consider your selection". "But I will tell you that I think it's time".
Haley, the former governor of SC, was a critic of Trump's during the 2016 Republican primaries and endorsed his opponent Sen. "They like her, except for maybe a couple, but that's normal", said Mr. Trump.
Responding to questions from the media, Haley made it clear that she has no intention of running for president in 2020, but instead intends to campaign for Trump for a second term. It will be a tough decision, he said, because Haley had made United Nations ambassador a more "glamorous" position than it had been in previous years.
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".
Trump also said on Tuesday his next meeting with North Korean leader Kim Jong-un is happening and officials are in the process of setting it up.
Republican lawmakers swiftly praised Mrs Haley after the news broke.
In April, Haley clashed with White House economic adviser Larry Kudlow over his suggestion she had suffered from "momentary confusion" when she announced that new sanctions against Russian Federation were imminent.
"Today's announcement that Ambassador Haley is resigning is yet another sign of the Trump Administration's chaotic foreign policy", he said in a statement".
Over the past two years, Haley became a critical voice for the White House's hardline approach against USA adversaries such as Iran and North Korea.
At the U.N., Haley helped spearhead the Trump administration's efforts to combat what it alleged to be anti-American and anti-Israel actions by the worldwide body. But Haley isn't a hardcore Trump loyalist, so why would he trust her with the Russiagate probe?
"I'm a lucky girl", she said at one point.
A rookie to worldwide politics, the former SC governor was an unusual pick for to be United Nations envoy. But Haley constantly denied it, saying she hadn't given any thought to a presidential run.
Despite Trump's calm words, her sudden announcement rattled a number in the White House, who openly speculated that the timing was meant to preserve the ambassador's own political future, according to the official and another White House official.