Honolulu City Councilman Charles Djou (R) was sworn in to the House of Representatives on Tuesday, three days after winning the special election in Hawaii.
"I want all the voters to know that every single day I have the privilege of serving them, I will never ever forget the trust and confidence they have vested in me," Djou said on the House floor before taking the oath of office.
Djou won the three-way race with 40 percent of the vote.
Democratic state Sen. Colleen Hanabusa finished with 31 percent, and former Rep. Ed Case (D) received 28 percent in the vote-by-mail election.
Djou fills the seat vacated by Rep. Neil Abercrombie (D), who resigned in February to concentrate on his gubernatorial bid.
Democrats have downplayed Djou's victory and have indicated they are confident they can win back the seat in November.
President Barack Obama grew up in the Honolulu district and received 70 percent of the vote there in 2008.