Nauert is a former Fox News Channel reporter who had little foreign policy experience before becoming State Department spokeswoman.
"I want to confirm that Bill Barr, one of the most respected jurists in the country, highly respected lawyer, former attorney general under the Bush administration, a terrific man, a terrific person, a brilliant man", Trumpsaid as he departed the White House.
She has been in her current role as spokeswoman for the US State Department since April 2017.
Heather Nauert, who earlier this year had been considered a possible successor to White House spokeswoman, Sarah Sanders, gained experience on diplomacy by working at the State Department, but she lacks the political and policy credentials of Ms Haley, who is a former governor of SC.
"In the past two years, we have worked closely with Ambassador Nikki Haley to change the hostile spirit in the United Nations, which has led to unprecedented achievements", Danon said.
Trump to nominate William Barr, former Bush 41 attorney general, for attorney general and Heather Nauert as the United Nations ambassador. The president, who puts a premium on loyalty, earlier hailed Nauert as "a supporter for a long time - really, excellent".
In her role, Nauert oversaw public diplomacy in Washington and all of the roughly 275 overseas US embassies, consulates and other posts.
The 48-year-old native of IL is deemed by State Department colleagues as "hard-working" and "well in over her head at an understaffed agency", reports by USA Today and Wbir suggest.
If Nauert is confirmed for the job, it would cap a precipitous rise in diplomacy in less than two years. But now, her experience in that State Department role is coming back to haunt her as well.
Nauert won't face an easy confirmation.
Speaking to Hindustan Times, a USA diplomat said, "Nauert seems to be a compromise candidate of two powerful foreign policy mavens of the Trump administration - Mike Pompeo and Bolton". 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.
"On another level, it's easily explained by Trump's fascination with American cable news, and in particular with Fox Cable News Network", the former Washington Bureau Chief for the Chicago Tribune said.
Trump is expected to make the announcement on Friday, the reports said.
Heritage Foundation fellow Brett Schaefer said Nauert has proven she has the ability to explain and defend USA foreign policy, the core requirement for being a US ambassador to the world body.
Pompeo tweeted that Nauert has traveled with him since he took the helm of the State Department.
But her inexperience sometimes shone through: in June she cited the D-day landings as evidence of the longstanding relationship between Washington and Berlin. But when White House officials told her they wanted her, she accepted.