Elected as the state's first female governor in 2010, she was in her second four-year term when Trump picked her. According to Swan, Haley told Trump she wanted to resign during a conversation with him last week.
Haley, often talked about as a future presidential candidate, and Trump spoke at a news conference after the announcement.
Trump did not offer further detail on why Haley is leaving, but her departure appears to be unusually amicable by the standards of his administration.
He said he would be naming her replacement in the next two to three weeks and that "very good people" were interested in taking up her role.
Haley has been a consistent "America First" voice on the global front, calling out United Nations' powers for anti-Israel, anti-West rhetoric.
The daughter of immigrants from India, Mrs Haley was a frequent and early critic of Mr Trump during his election campaign whilst she served as the Republican governor of SC.
"I don't see (my role) as pushing an "America First" policy, I see it as defending America because every day I feel like I put body armor on". "I'll never truly step aside from fighting for our country. I think it's time".
She also hailed the president's brand of unilateral foreign policy. We passed the toughest sanctions against any country in a generation, pressuring North Korea toward denuclearization.
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"She got to know the players, she got to know China, Russia, and India.they like her...they respect her".
Yet, in the wake of her resignation, two sources familiar with Haley's relationship with Trump told CNN that she had lost clout with the President in recent months. 'I can promise you what I'll be doing is campaigning for this one.
The announcement was news to many congressional Republicans involved in foreign policy matters, and some key US allies did not get advance word from Haley or the White House. So I look forward to supporting the president in the next election'. When there is disagreement, there is a right way and a wrong way to address it. "I pick up the phone and call him or meet with him in person", she wrote.
It became Haley's defining characteristic.
Haley thanked the president, saying that the U.S.is finally "respected" on the world stage. The retort quickly earned her an apology.
"Before she was named by Trump to her United Nations post, Haley was elected the first female governor of SC". Marco Rubio (R., Fla.). When a White House adviser said Haley had been confused in prematurely announcing more sanctions against Russian Federation, she said simply, "With all due respect, I don't get confused".
It remains unclear what prompted Ms. Haley to quit and who will succeed her at as ambassador to the UN.