Ms Power is an Irish-American and long-time human rights advocate, who served as US ambassador to the United Nations under former President Barack Obama and then-Vice President Biden from 2013 to 2017.
“Power will rally the international community and work with our partners to confront the biggest challenges of our time — including Covid-19, climate change, global poverty, and democratic backsliding,” Mr Biden’s transition team said in a statement.
“A crisis-tested public servant and diplomat, Ambassador Power has been a leader in marshalling the world to resolve long-running conflicts, respond to humanitarian emergencies, defend human dignity, and strengthen the rule of law and democracy,” it added.
Ms Power, 50, also served as a White House national security staffer under Obama from 2009 to 2013.
A former journalist, she won a Pulitzer Prize for her book “A Problem from Hell,” a study of US failure to prevent genocide.