Results posted on the state Secretary of State's website indicated Sinema received 100,486 votes, or 48.13 percent, to Vernon Parker's 94,697 votes, or 45.35 percent in the state's 9th Congressional District, a district created as a result of the 2010 Census.
"We've made history, and we're proud of that," Sinema told ABCNews.com Monday. "But what I am interested in is making history by making things better for the people of Arizona's 9th Congressional District."
Sinema, a former state lawmaker, joins at least five openly gay Democrats elected to the House this year. Sen.-elect Tammy Baldwin, D-Wis., a former House member, became the first openly gay candidate elected to the U.S. Senate.
Sinema said she believes voters in the district, which encompasses a portion of Phoenix's suburbs, responded well to her platform that included creating jobs in Arizona.
"My own family, my own life has been the struggle of making it to the middle class," she told ABCNews.com. "This district is a very young district. We'll always be competitive. Folks will be making decisions on who has the best ideas."