Even with the advantage in name id and fundraising, Allen faces what could be a tough Republican primary.
Tea Party activist Jamie Radtke is already in the contest and used Allen's entrance into the race Monday to again challenge him to weekly town hall forums across the state.
Radtke has slammed Allen's fiscal record in the Senate and also called on him Monday to "explain his record on deficit
"Twelve years ago when George Allen was running for the U.S. Senate, he pledged his commitment to a balanced budget, reducing spending and reducing the debt," Radtke said in a statement. "Then he went to Washington and voted for spending measures that increased our national debt by $3.1 trillion and voted for $90 billion in earmarks."
Radtke also received a boost of support from conservative blogger Erick Erickson Monday, who warned on RedState that Allen's record is "out of step with most of the grassroots activists engaged in Republican primaries today."
In a statement, Allen spokeswoman Katie Wright said the former senator looks forward to "a spirited campaign."
"George Allen has attended hundreds of town halls, rallies and meetings across Virginia listening to the concerns of Virginians worried that Washington is ignoring their views and values," Wright said. "He looks forward to a spirited campaign to discuss the issues important to Virginians like balancing our budget, repealing and replacing health care, and creating opportunities for more jobs."
-Updated at 4:21 p.m.