Nauert did not respond to requests for comment.
She'll also take up the administration's efforts to defend Israel at the United Nations and counter what Haley called the organization's bias against the Jewish state.
Nauert became the state department spokeswoman in April 2017 and this year was named the acting undersecretary for public diplomacy and public affairs. The officials were not authorized to speak publicly before Trump's announcement.
A former news reporter for ABC, she joined Fox in 1996, originally as a correspondent and later as a co-host for Fox and Friends.
Nauert's appointment was first reported by Bloomberg.
Experience matters less to the President, an avid fan of Fox News, than Nauert's loyalty to the White House, the fact that she's a woman and her ability to be a polished proxy on television, according to sources familiar with his thinking.
Trump expected to pick State spokeswoman for UN ambassador
He pulled the United States out of the U.N. human rights body in September, citing bias toward Israel, and his administration has cut funding for the U.N. refugee agency and previous year proposed US funding cuts for aid and diplomacy that could curb the work of the global body. Haley, former governor of the U.S. state of SC, said she did not know what she would do next, but clarified that she would campaign for Trump ahead of the 2020 presidential election.
Nauert would take up the US mantle at the United Nations including holding sanctions on North Korea and defending Israel.
Trump is reportedly weighing other staff changes before the end of the year, including replacing White House Chief of Staff John Kelly.
If she wins Senate confirmation, Nauert will face a broad agenda at the United Nations topped by the need to maintain global sanctions on North Korea.
"She is clearly not qualified for this job, but these days it seems that the most important qualification is that you show up on Donald Trump's TV screen, and if you're successful in that endeavor, then you seem to be a top candidate to get a whole bunch of top positions in the US government".
Nauert, left, and White House press secretary Sarah Sanders.