She faced Republican Betty Chu, a cousin of hers by marriage, and Libertarian candidate Christopher Agrella.
The predominantly Democratic 32nd district includes Rosemead, El Monte, Baldwin Park, Irwindale, Covina and Walnut Valley.
Chu is a former state Assembly member and will become Southern California's only Asian-American in Congress.
Chu won 60 percent of the votes Tuesday night and will give Democrats a 256-178 edge over Republicans in the house.
Chu could be sworn in as early as Thursday.
The Associated Press contributed to this report.