The Richmond Times-Dispatch said with nearly half of precincts reporting, Allen had 65 percent of the vote to 24 percent for Jamie Radtke, 5.6 percent for state Delegate Robert Marshall and 4.7 percent for E.W. Jackson.
Allen will go up against Democratic former Gov. Timothy M. Kaine in November's general election. The winner will take the seat held by Democratic Sen. Jim Webb, who defeated Allen in 2006 but decided not to seek re-election.
"Voters already had the chance to experience George Allen's vision during his last term in the Senate, which turned record surpluses into massive deficits, added trillions to our debt, and put opportunity for a select few ahead of opportunity for all our businesses and families," Kaine said in a statement. "George Allen's approach helped create our economic mess; Virginians can't afford six more years."
U.S. House Majority Leader Eric Cantor and fellow Republican Rep. J. Randy Forbes easily defeated their primary opponents.
"We are in a fight to reclaim this country, to put America back on track," Cantor said. "All eyes will be on the commonwealth and we're going to make the difference."