The latter is Trump's favorite cable news network, which helped her land the State Department job.
He told reporters at the White House that she is 'very talented, very smart, very quick.
Nauert, a native of Rockford, Illinois, worked at State as the acting undersecretary for public diplomacy and public affairs.
Assuming that Nauert wins Senate approval after her upcoming confirmation hearing, the United Nations post will be her first policy role in the USA government.
Trump's decision was first reported by Bloomberg News and if confirmed Nauert is likely face a "tough" Senate confirmation hearing.
"It will have to do with the Joint Chiefs of Staff, and succession", Mr. Trump said.
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The president, who puts a premium on loyalty, earlier hailed Nauert as "a supporter for a long time - really, excellent". "Ambassador Haley will always be a true friend of the State of Israel".
According to reporting by CNN's Kaitlan Collins, Secretary of State Mike Pompeo has told aides he wants the position downgraded from Cabinet level, which is in line with previous Republican administrations. Whereas Haley said she would remain gruff against Kim Jong Un furthering any missile testing, it remains to be seen if Nauert would do the same.
Unlike Haley, however, Nauert is not expected to have cabinet status, keeping power over foreign policy firmly with Pompeo and especially John Bolton, the hawkish White House national security advisor. She also would be going up against foreign counterparts like the United Nations representatives from Russian Federation and China, who each have decades of experience in diplomacy.
While Nauert struggled during the tenure of former Secretary of State Rex Tillerson - so ostracized from his inner circle that she considered quitting - she could now bring to the United Nations close ties to the White House and a good working relationship with Secretary of State Mike Pompeo.
Haley, in what could be a final diplomatic push, on Thursday failed in a bid for the UN General Assembly to condemn the Palestinian Hamas movement for firing rockets at Israel. "Heather plays a key role in advancing US foreign policy & I look forward to her speedy confirmation".
Pompeo tweeted that Nauert has travelled with him since he took the helm of the State Department.
Shortly after Trump made the pick official, The Washington Post flagged an exchange from earlier this year in which Nauert cited the D-Day invasion as an example of the "strong relationship" between the United States and Germany. Before joining the State Department she worked as an anchor for Fox News and correspondent for ABC News.