Becker was sworn in by chief justice Michael Bender before an audience of her family and several legislators.
The newest member of the House of Representatives will leave her seat on the Boulder City Council. An attorney, Becker once worked for the U.S. Department of Interior.
Former Rep. Claire Levy, D-Boulder, resigned the District 13 seat to take a position as executive director of the Colorado Center on Law and Policy. Levy was in her last term as a state representative, having been first elected in Nov. 2006.