If confirmed by the Senate, Nauert would assume the U.S. ambassador job at the end of the year.
Nauert has been a news correspondent since 1998, mostly at Fox News. She primarily worked as a health insurance consultant in Washington, D.C., and became a spokeswoman for the State Department in April 2017.
"She's going to work with Nikki Haley to replace Nikki at the United Nations," Trump told reporters at the White House Friday. "She's very talented, very smart, very quick, and I think she's going to be respected by all."
When former Secretary of State Rex Tillerson was fired earlier this year, Nauert was promoted to acting under secretary of state for public diplomacy and public affairs. In October, she lost that title but kept the responsibilities.
When Nauert's name came up last month as a potential replacement for Haley, Trump praised her.
"She's been a supporter for a long time, and she's really excellent," he said then.
Haley announced in October she would resign at the end of the year. She called the job an honor of a lifetime and said she wants to let someone else take it.
"My goal is that we make sure everything is in a good place for the next ambassador to come in," Haley told reporters in October.
Haley also dismissed the possibility of running for president in 2020, saying she will support Trump's re-election campaign.