LOS ANGELES—Democrat Katie Hill captured the last Republican-held House seat anchored in Los Angeles County on Friday, padding the Democrats’ advantage in the chamber next year.

Hill ousted Republican Steve Knight, who was seeking a third term in the 25th District that cuts through suburbs, horse ranches and high desert in northern Los Angeles County and a slice of Ventura County.

Knight conceded the race Wednesday, saying “the voters have spoken.” Hill maintained her election night lead after further vote counts were released Friday.

A political newcomer, Hill promised to end politics as usual and stressed her centrist politics: She’s a gun owner and her Republican father is a police officer who had never voted for a Democrat before her primary. Her mother, a Democrat, is a nurse.

Hill, 31, who worked as an executive for a group providing services for the homeless, supports universal health care and counts Massachusetts Sen. Elizabeth Warren, a liberal favourite, among her supporters. But she also highlighted her family’s military service and says immigration policy must start with securing the nation’s borders, echoing a familiar Republican refrain.

Her endorsements run from firefighters to unions to Equality California, an LGBT advocacy organization. Hill is married and openly bisexual.