With 84.65 percent of precincts reporting, Kirk has captured 61 percent of the vote, beating out five other Republican opponents: John Arrington, Don Lowery, Andy Martin, Kathleen Thomas and Patrick Hughes.
"This election means we will not surrender to [the Democrats'] dangerous cynicism of low expectations," said Kirk in his acceptance speech.
His Democratic opponent in November's general election will be Illinois Treasurer Alexi Giannoulias, who wrapped up the democratic nomination.
Kirk currently represents the 10th Congressional District located in the north suburbs of Chicago. He is a member of the House Appropriations Committee and is co-chairman of the moderate GOP Tuesday Group and the bipartisan House US-China Working Group.
Kirk cast his ballot earlier Tuesday at the Highwood Recreation Center and is holding his election night gathering at the Westin Chicago North Shore hotel in Wheeling.