Nauert's nomination had been rumoured for weeks, and she had started handing over some of her responsibilities as spokeswoman to her deputy, Robert Palladino.
ABC News reported in November that Ms Nauert had been offered the job, but it was not clear at the time whether she had accepted.
According to multiple sources, the president will bring Heather Nauert from her current position as State Department spokeswoman to replace Haley at the United Nations.
Nauert, 48, worked as a Fox News host prior to her role in the State Department.
Sources told Fox News Thursday evening that he will announce his decision in a tweet Friday.
Trump expected to pick State spokeswoman for UN ambassador
Nonetheless, during her two-year stint, Haley became a darling of the Trump administration and the pro-Israel community for her vociferous defense of the Jewish state at the United Nations, a body often seen as hostile to Israel.
Nauert was named as the State Department spokeswoman in April 2017.
Nauert's appointment was first reported by Bloomberg.
If Ms Nauert passes the Senate confirmation and subsequently assumes the role, her top priority will be to maintain sanctions on North Korea, which her predecessor managed to rally global support for previous year when Kim Jong-Un was conducting his ballistic missile testing.
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.
Two of Mr Trump's advisers have said he is weighing a number of other end-of-year staff changes, including replacing Chief of Staff, John Kelly. 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.A graduate of Keith Country Day School in Rockford, Nauert is the daughter of the late Peter W. Nauert who led Pioneer Life Insurance Co. of IL.More news: Arrest in Australian cold case made famous by podcast