"I come to the UN not only as the president's emissary but as a voice of America's unwavering commitment to democracy, freedom, human rights and, whenever possible, the peaceful resolution of conflicts," Kelly Craft told reporters on Thursday.
The 57-year-old Republican Party activist and donor, who served previously as ambassador to Canada, was confirmed by the Senate in July as the permanent successor to former South Carolina Gov. Nikki Haley, one of the most prominent figures in the Trump administration, Efe news reported.
Following Haley, who arrived at the UN threatening reprisals against countries who failed to toe Washington's line, Craft took a more diplomatic approach in her debut at the world body.
"I will defend America's values and interest. I will stand by our friends and allies. I will advocate for the poor and weak," Craft said.
Lauding the "noble mission" of the UN, the new US envoy likewise praised Secretary-General Antonio Guterres as a wise and "visionary" man.
Craft presented her credentials to Guterres prior to taking part in her first Security Council meeting.
"In a world marked by humanitarian crises and geopolitical challenges, strong American leadership is absolutely critical and I intend to provide it," she said.
The new US ambassador to the UN also spoke of her "extraordinary gratitude for the bold leadership" of Trump.
Haley stepped down last December and the president's first choice to succeed her was Heather Nauert, a former Fox News host who then held the post of State Department spokeswoman.
But Nauert withdrew her name from consideration in February after it became clear that her previous employment of a nanny who did not have a US work permit was going to be an issue in the Senate confirmation process.
Craft and her husband, billionaire coal executive Joe Craft, donated roughly $1.5 million to Republican candidates in 2016, including some $270,000 in contributions to the Trump campaign.
The couple are also on a VIP list of frequent guests at the Trump Hotel in Washington.
Politico reports that Joe Craft contributed $1 million to defray the costs of Trump's inauguration.