Haley cited Trump's tough trade policy, his decision to leave the Iran nuclear deal and move the U.S. Embassy in Israel to Jerusalem, which infuriated many allies and regional partners.
"I will support the president", Haley said.
She has been more outspoken in calling out Russian aggression than Trump, for example. She spoke out against racism and on issues of gender.
Trump at one point said Haley would be welcome back to the administration any time - a remark that caused her to break into good-natured laughter.
In recent months, her star had faded a bit, with Tillerson replaced by the brash Mike Pompeo and John Bolton taking over as national security advisor.
But, as she said herself, she had a track record in shaking up staid, traditional government bodies - a quality that surely appealed to Trump.
5000 feared missing as search for Indonesia quake victims continues
Aid has been slow to reach survivors, and desperate villagers have stormed into shops to grab food supplies. He says how many plane loads of aid fly from Darwin will depend on future Indonesian requests for help.
"Well, I had a personal conversation with the president about Charlottesville, and I will leave it at that", Haley told CNN's Dana Bash at the time. When the sanctions never materialized, White House officials said the plans had changed without Haley being briefed, and top economic adviser Larry Kudlow suggested Haley was confused.
Speaking in the Oval Office, he said: 'Nikki Haley has been very special to me...
Haley was appointed to the U.N. post in November 2016 and last month coordinated Trump's second trip to the United Nations, including his first time chairing the U.N. Security Council. After running for the SC legislature in 2004, Haley, who is married to U.S National Guard office, became only the second Indian-American government of a U.S state (after Bobby Jindal) in 2010. She cited US action on Syrian chemical weapons, trade deals, the arms embargo in South Sudan, U.N. sanctions against North Korea, pulling out of the Iran nuclear deal and moving the USA embassy in Israel to Jerusalem.
Her most visible role, however, is likely to be remembered as pulling the US out of the U.N. Human Rights Council, which she described as a "cesspool of political bias" against the USA and Israel. At this time, there's no word on who could replace Haley as United Nations ambassador, but her successor should be named within two to three weeks, according to the president. "Her news shocked a number of senior foreign policy officials in the Trump administration".
Haley called serving as United Nations ambassador "an honor of a lifetime", but added that it was time for her to depart the administration. "I don't agree with the president on everything".
"Nikki Haley has been a clear, consistent, and powerful voice for America's interests and democratic principles on the world stage".