Republican Congressman Frank Wolf, who currently represents the 10th congressional District, recently announced his retirement from Congress.
Foust, a resident of McLean, has represented the Dranesville district since 2007; he was re-elected in 2011. He held a fundraiser at his home on Jan. 3.
Other Democrats running for the congressional district, which includes McLean, Ashburn, Leesburg, Chantilly and Manassas, are lawyer Richard Bolger, architect Sam Kubba and former Marine Corps Capt. David Wroblewski.
State Sen. Richard H. Black, R-Loudoun, recently decided not to seek the GOP nomination, which could help the chances of Del. Barbara J. Comstock, R-Fairfax.
Richard Shickle, chairman of the Frederick County Board of Supervisors, also is seeking the Republican nomination.
Republicans will meet April 26 in a party canvass to choose their nominee, while Democrats will make their decision this week on a nominating method.