Republican candidate Juan Ciscomani was declared the winner of the Congressional District 6 race on Monday night by the Associated Press.
Ciscomani will replace Democratic Rep. Ann Kirkpatrick who is retiring.
The district is considered highly competitive. It was redrawn by the Independent Redistricting Commission to include eastern Pima County, much of Cochise County, and parts of Graham, Greenlee, and Pinal Counties.
As of Monday night, 341,072 votes were counted in the district. Ciscomani leads his Democratic opponent Kirsten Engel by 3,502.
Ciscomani's win cements a 6-3 Republican majority in Arizona's congressional delegation and helps the GOP's efforts to take control of the House. On Friday, three-term Democratic Rep. Tom O'Halleran lost to businessman and former Navy Seal Eli Crane in the 2nd District.
The Associated Press contributed to this story.