Linda Thomas-Greenfield was sworn in on Wednesday as the United States ambassador to the United Nations.
Thomas-Greenfield took her oath of office before Vice President Kamala Harris.
Her inauguration followed a confirmation vote by the senate on Tuesday. The diplomat who was Assistant Secretary of State for Africa under the administration of Barack Obama was confirmed by 78 votes to 20 in the upper house, which has the power to approve or reject presidential nominations.
At the UN in New York, expectations are high for the new ambassador, whose portfolio has been elevated to a ministerial rank.
Thomas-Greenfield, a respected career ambassador, was one of President Joe Biden's first picks for his national security team. An Africa specialist, she served as U.S. ambassador to Liberia, and held posts in Kenya, The Gambia and Nigeria.
She was expected to travel New York, the seat of the United Nations, to present her credentials to UN Secretary General António Guterres on Thursday.
She is the third African-American, and the second African-American woman, to hold the U.N. post.
Observers have said that Washington's influence at athe United Nations diminished under Donald Trump.
Trumped pulled the US out of key agaencies such as UNESCO and the World Health Organization and reneged on key international agreements such as the Iran nuclear deal and the Paris Climate Accord, as he promoted his America First policy.