Physicist Ernest Moniz is a professor at the Massachusetts Institute of Technology. Moniz replaces Steven Chu, who served as energy secretary in Obama's first term.
Moniz was an energy undersecretary in the Clinton administration.
Republican Senator Lindsey Graham had delayed a vote on Moniz for several weeks. Graham was protesting Obama's plan to cut about USD 200 million from a South Carolina project to turn weapons-grade plutonium into fuel for nuclear reactors.
Graham and other Republican lawmakers said the plan jeopardised a plant being built at the Savannah River nuclear site.