The Senate on Wednesday confirmed Samantha Power, a human-rights activist and President Barack Obama’s ambassador to the United Nations, to lead the U.S. Agency for International Development.

By a vote of 68-26, the Senate confirmed Ms. Power to lead an agency that is one of the world’s largest distributors of humanitarian aid. Ms. Power is expected to have a seat on the National Security Council, which she also held during the Obama administration.

Pooja Jhunjhunwala, the acting spokeswoman for U.S.A.I.D., said that Ms. Power will be sworn in on Monday.

Ms. Power arrives at a time when the agency will be focused on combating poverty and disease across the world in places that have been severely affected by the coronavirus pandemic. In nominating Ms. Power, the Biden administration has signaled that U.S. foreign aid will serve as a pillar of soft-power diplomacy.

During her confirmation hearing in March, Ms. Power said she would use the agency to combat China’s influence in regions including Africa, Eastern Europe and South America, warning that Beijing is using its prominence on the global stage in a “predatory way” that flouts diplomatic norms.

Ms. Power, a former war correspondent, rose to prominence as an academic focused on genocide prevention. She has been viewed as an unabashed humanitarian, one who has advocated for military intervention to reduce civilian suffering, most notably in Libya and Syria.

Human rights activists said that Ms. Power will face a tough road ahead, as the pandemic lays bare disparities across the world.

“Administrator Power arrives at U.S.A.I.D. at a challenging time,” said Tom Hart, acting chief executive of the ONE Campaign, an anti-poverty group. “We’re at risk of seeing one pandemic with two futures: one for wealthy countries who can get vaccines and can afford economic stimulus and those who can’t.”