The state highway runs 29.27 miles (47.11 km) from U.S. Route 1 (US 1) in Woodbridge north to the Chain Bridge across the Potomac River into Washington from Arlington.

After leaving the Town of Vienna, the name reverts to Chain Bridge Road, and continues this way until the intersection with I-495 in Tysons.

SR 123 is a partial circumferential highway in Northern Virginia that connects Woodbridge in eastern Prince William County with the independent city of Fairfax and the Fairfax County communities of Vienna, Tysons, and McLean, the last being the home of the National Counterterrorism Center and the Central Intelligence Agency.

SR 123 meets I-95 at a partial cloverleaf interchange that contains a reversible ramp to and from the Interstate's HOV lanes in the direction of Washington.

The Route 123 and I-95 Commuter Lot, a park and ride facility, is located within the southeast quadrant of this interchange.

The state highway passes by the former Lorton Reformatory and reduces to four lanes north of SR 611 (Furnace Road).

SR 123 passes northwest along the edge of the suburban communities of Laurel Hill, Crosspointe, and South Run.

North of University Drive, SR 123 enters the city of Fairfax and its name changes to Chain Bridge Road.

The state highway curves northeast through Oakton, then enters the town of Vienna and becomes four-lane undivided Maple Avenue just south of its intersection with SR 243 (Nutley Street).

[1][3] At the eastern edge of Tysons, SR 123 passes under Westpark Drive has a cloverleaf interchange with I-495 (Capital Beltway).

[1][3] East of the center of McLean, SR 123 passes by the preserved Salona estate and close to Hickory Hill—a historic house on Chain Bridge Road that was home to Robert F. Kennedy—in Langley, where the state highway meets the eastern end of SR 193 (Old Georgetown Pike).

East of its partial cloverleaf interchange with the George Washington Memorial Parkway, the state highway's name becomes Chain Bridge Road and reduces to two lanes as it descends into the valley of the Potomac River.

Fairfax County DOT has also considered building pedestrian space over the intersection, such as a park, to improve walkability in Tysons Corner.