Trump told reporters that Nauert, who is in line to take over from Nikki Haley, had proven herself as a "very talented, very smart" member of his administration.
Nauert, 48, had been touted for the post since October when Haley announced that she was stepping down.
US State Dept spokesperson Heather Nauert could be next UN ambassador
She has served under two secretaries of state —Rex Tillerson and her current boss Mike Pompeo — and was designated acting under-secretary for public diplomacy and public affairs from March to October 2018.
Haley similarly had little foreign policy experience when appointed, although she had a national name as the governor of South Carolina.
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.
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