The US Senate voted on Wednesday to confirm Samantha Power, Washington's former envoy to the UN, to lead the US Agency for International Development (USAID).
Ms Power, who was nominated by President Joe Biden, was confirmed with backing from Republican and Democratic politicians, with 68 supporters and 26 votes against.
The Irish-American academic and author of a Pulitzer Prize-winning book about genocide, A Problem from Hell, said she looked forward to leading the $41 billion-budget agency.
“Confirmed!” she posted on Twitter. “Thank you everyone for your support these last months. I’m so grateful for this bipartisan vote of confidence from the Senate, and so energised to be joining the incredible @USAID team to get big things done.”
Ms Power, 50, a long-time human rights advocate, is a public policy professor at the Harvard Kennedy School and also served on the National Security Council.
Bob Menendez, chair of the Senate Foreign Relations Committee, said she was the right choice to lead an agency that operates across more than 100 countries.
"I'm confident her experience, tenacity and drive to build a better, more prosperous, peaceful world are exactly what USAID and our country need at this moment," Mr Menendez said.
As former president Barack Obama’s UN ambassador from 2013 to 2017, Ms Power worked on the fight against Ebola, the 2015 Paris Agreement on climate change, tackling poverty and shutting down financing for ISIS.
Ms Power, an advocate of Western-led military intervention to stop atrocities, famously sparred with Mr Obama over the civil war in Syria, notably when he did not use force against the regime, which began increasing its use of chemical weapons in 2013.
She was instrumental in the 2014 UN Security Council decision to open four border crossings into Syria from Turkey, Iraq and Jordan to get aid into rebel-held areas, even while Damascus denounced it as a breach of Syria’s sovereignty.
The Senate on Wednesday also voted to confirm Colin Kahl as the Defence Department’s policy chief, moving past objections from Republicans on his possible disclosure of classified information on social media and his role in negotiating the 2015 Iran nuclear deal.