Route 7 enters Loudoun County in Sterling as Harry F. Byrd Highway and widens to six lanes throughout the first half of the county. Route 7 passes by numerous subdivisions and strip malls before its interchange with State Route 28.

From there, Route 7 passes through Ashburn, across Goose Creek, and into Leesburg, the county seat of Loudoun County. Route 7 is planned as an eight-lane, limited access highway through this portion of the county. Currently, interchanges are under design for the signalized intersections at Loudoun County Parkway and Ashburn Village Boulevard. Additional interchanges are planned for the signalized intersections at Sycolin Road, Battlefield Parkway, and Belmont Ridge Road.

In Leesburg, Route 7 splits into a business route and bypass. The bypass merges with the U.S. Route 15 bypass around the southern half of the town, while the business route passes through the town and intersects Business 15 at the county court house in downtown Leesburg.

 

Business and Bypass 7 meet on the western side of Leesburg, and continues into rural western Loudoun as a four-lane divided highway with some at-grade intersections before its interchange with Route 9. After passing through Clarke's Gap in Catoctin Mountain, Route 7 has an interchange with State Route 9 in Paeonian Springs . The interchange is the southern terminus of Route 9, as well as the eastern terminus of another Business Route 7. Business Route 7 serves the towns of Hamilton, Purcellville, and Round Hill. The bypass maintains a 55 mph (89 km/h) speed limit as a divided limited-access highway.

After Round Hill, Route 7 is no longer a limited-access highway, but maintains a 55 mph (89 km/h) speed limit. As the road approaches the western edge of the county, it curves around a corner of West Virginia, passes through the town of Bluemont (formerly Snickersville), meets the Snickersville Turnpike and climbs the Blue Ridge, passing through Snickers Gap.