Mr Waxman could help Barack Obama pass climate change legislation
US Congressman Henry Waxman has unseated John Dingell to become chair of the powerful energy committee of the House of Representatives.
Democratic members of Congress voted 137 to 122 for Mr Waxman, 69, to take up the committee chairmanship.
Mr Dingell, 82, a representative from Michigan, had been viewed as a strong ally of the US car industry.
Mr Waxman, who represents a California district, is a keen proponent of measures to ease global warming.
Incoming president Barack Obama has indicated that he will make tackling climate change a top priority.
The BBC's Adam Brookes, in Washington, says Mr Obama may now find it easier to get his environmental agenda through Congress with Mr Waxman in such a powerful position.
Mr Dingell, with his links to the automobile lobby, had been viewed as an obstacle to the progress of climate change legislation, our correspondent adds.