It's unclear why Haley resigned.
He called Haley a "very special" person, adding that she told him six months ago that she might want to take some time off. Trump said that together they had "solved a lot of problems". And when Haley delivered the GOP's response to President Obama's last State of the Union address in January 2016, she all but begged Americans to run away from Trump's narrow-mindedness and demagoguery.
In one noticeable instance, Haley gave a press conference in front of missile parts she said were provided to Yemeni rebels by Iran, a charge denied by Tehran.
Instead of answering directly, he recounted how she has had to work on tough issues, such as Iran and North Korea.
If this was long-planned, it was apparently the best-kept secret in Trump's White House.
"Look at the two years, look at what has happened in two years with the United States on foreign policy. Jared and I are grateful for her friendship - a true blessing in our lives!"
Ivanka and her husband Jared Kushner both work in the White House as high-level unpaid advisers.
"I don't get confused", Haley said in a sharply-worded rejoinder to the West Wing.
Sanford, a fellow former SC governor who has been allies with Haley in the past but is now an administration critic, said of the story: "Something doesn't smell right". At the United Nations, she helped spearhead the administration's efforts to combat what it alleged to be anti-American and anti-Israel actions by the global body, and address US tension with its European allies and with Iran and North Korea. Haley's biggest accomplishment on the Security Council, attaining Russia and China's consensus on a increasingly stringent sanctions resolutions against North Korea, are now being undercut by those very same countries-ship-to-ship transfers of illicit goods on the high seas by the Chinese and open ports courtesy of the Russians.
And even if 2020 isn't an option, Ms Haley is only 46-years-old.
Trump said he was considering many candidates for Haley's job and that a successor would be named in two to three weeks.
Haley discussed her resignation with Trump last week when she visited him at the White House, Axios news site reported.
Dina Powell served in the first year of the Trump administration as the Deputy National Security Adviser. U.S. Ambassador to the Germany Richard Grenell's name has also been floated for the post, according to an administration official.
The daughter of Indian immigrants, Haley clashed with then-candidate Trump during the 2016 campaign, denouncing "the siren call of the angriest voices" who disrespected America's immigrants. Another possible explanation was her desire to earn more money in the private sector to pay down debt and put her children through school. Trump tweeted that "The people of SC are embarrassed by Nikki Haley". "She is a bold reformer and has been an unwavering champion of truth, principled realism and integrity within the United Nations".
She outlasted Trump's first secretary of state, Rex Tillerson, who, unlike Haley, generated friction with Trump: on substance, on style, on mannerisms, and other matters. As governor, she developed a national reputation as a racial conciliator who helped lead the effort to bring down the Confederate flag at the Statehouse and helped guide the state through one of its darkest moments, the massacre at a black church.