Stefanik, 30, defeated Democratic challenger Aaron Woolf and Green Party challenger Matthew Funiciello. The Associated Press called the race in her favor with 68 percent of precincts reporting and Stefanik winning 55.9 percent of the vote compared to Woolf's 32.4 percent.
Stefanik had previously worked on former GOP presidential candidate Tim Pawlenty's 2012 campaign. She's a Harvard graduate.
Democrat Bill Owens, who is retiring, currently holds the seat.