Trump's announcement comes just a day after the US lost a high-profile vote in the U.N. General Assembly for a resolution condemning the Palestinian militant group Hamas.
File photo of Heather Nauert.
Like Haley, a former SC governor, Nauert would come to the job with little experience in diplomacy.
Nauert is a native of Rockford, Illinois. With a master's degree from Columbia University's Graduate School of Journalism, she had come to Fox from ABC News, where she was a general assignment reporter.
Before joining the State Department, Nauert did not have any previous government or diplomatic experience.
Nauert's appointment would reinforce the link between Fox News and Trump, who has been accused of turning to the conservative-leaning channel, rather than experts, for policy advice. That means Nauert could be overshadowed by Pompeo or Trump's national security adviser, John Bolton, who had the United Nations job in 2005 and 2006. Previously, she was a Fox News presenter and correspondent. In October, she lost that title but kept the responsibilities.
Is Nauert up for the new role? According to The Guardian, the President has sought someone who will "demonstrate loyalty".
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Fox News has been a consistent supporter of the president and he often cites its news.
Although some have speculated that Haley may challenge Trump in the 2020 presidential election, Haley has said that she will support the president.
Plucked from Fox to be the State Department's public face, Nauert catapulted into the upper echelons of the agency's hierarchy when Rex Tillerson was sacked in March and replaced with Mike Pompeo.
"When you talk about Germany, we have a very strong relationship with the Government of Germany", Nauert said, and mentioned the anniversary of the post-World War II Marshall Plan.
She would be taking the position amid a roster of thorny global challenges, ranging from North Korea's nuclear program to Yemen's starvation and the growing divide between the USA and its closest allies over the Iran nuclear deal, climate change and other issues.
That means Nauert would wield less clout than her predecessor, both at the United Nations and within the administration, and as a result, would pose nowhere near the challenge to national security adviser John Bolton, White House chief of staff John Kelly or Pompeo.
It was unclear whether the United Nations ambassador post would remain part of the Cabinet, as it has been under Ms Haley, and there have been internal discussions about not having it remain a Cabinet-level position, one White House official said. Nauert's performance as acting undersecretary of state was notable for its lack of accomplishments or even attention to the job.