Nevertheless, the announcement surprised many in the Trump administration.
At the recent UN General Assembly session, Haley took the highly unusual step for a senior diplomat of joining street protesters against Venezuelan President Nicolas Maduro, shouting from a megaphone that the leftist leader should leave office. "But I will tell you that I think it's time".
On Monday, the federal watchdog group Citizens for Responsibility and Ethics in Washington (CREW) called for the State Department's inspector general to launch an ethics investigation into Haley, regarding seven free flights on private planes that Haley and her husband accepted from three SC businessmen in 2017.
"I have given everything I've got these last eight years", she said, referring to her six years as SC governor as well as her time at the United Nations.
Haley gave no specific reason for leaving, saying she didn't have "anything set, ' adding that she believed in 'term limits" and letting someone else take on the challenging post.
"She's done a fantastic job, and we've done a fantastic job together", Trump said, adding that he'd be happy to have her back in another position.
Haley was appointed to the United Nations post in November 2016.
"I'm such a lucky girl to have been able to lead the state that raised me and to serve a country I love so very much has really been a blessing, and I want to thank you for that", she told Trump. But the group, Citizens for Responsibility and Ethics in Washington, said in its complaint that Haley's financial disclosure did not provide enough information to make the assertion that the flights between New York, Washington, DC, and three SC cities qualified for the exemption. "We will miss you... you've done a fantastic job", Trump said in warm words that clearly showed there was no animus between them.
Tuesday's announcement prompted widespread praise of Haley's tenure from fellow Republicans, but some lawmakers expressed concerns about the timing.
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.
Haley, 46, is the latest in a long line of high-profile departures from the administration, such as former Secretary of State Rex Tillerson, who was sacked in March, and Steve Bannon, Trump's chief strategist, who left in August 2017.
As it turned out, Haley suggested her departure was no more than a case of burnout. She spoke out against racism and on issues of gender. At the beginning, North Korea was a massive problem, and now we're moving along.
"The US is strong again.in a way that should make all Americans proud", she said.
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.
CNN has referred to her as "the breakout star" of Trump's cabinet. "As a private citizen, I look forward to supporting your re-election as President, and supporting the policies that will continue to move our country toward even greater heights".
Haley, a rookie to worldwide politics, was an unusual pick for to be United Nations envoy. The president said Haley has been very special to him, and they will be in constant touch.