Known for most of its length as Old Dominion Drive, which was once the right of way of the Great Falls Division of the Washington and Old Dominion Railroad, the state highway runs 5.33 miles (8.58 km) from SR 123 in McLean east to U.S. Route 29 (US 29) in Arlington.

Old Dominion Drive continues northwest as SR 738 toward Great Falls.

Shortly after entering the latter county, SR 309 expands to a four-lane divided street and intersects SR 120 (Glebe Road) at an oblique intersection adjacent to Marymount University; at the south end of the intersection, the two highways cross over Yorktown Boulevard.

SR 309 briefly runs concurrently with US 29 as four-lane divided Old Dominion Drive.

Within Arlington's Cherrydale neighborhood, SR 309 reaches its eastern terminus at a five-way intersection with US 29, Quincy Street, and Military Road.