Known also as Fairfax Pike and Fairfax Street, the state highway runs 4.72 miles (7.60 km) from U.S. Route 11 and SR 631 in Stephens City in southern Frederick County east to US 522 and US 340 at Double Tollgate in the southwestern corner of Clarke County.

SR 631 (Fairfax Street) continues west from the intersection through the Newtown-Stephensburg Historic District and out of town toward the village of Marlboro.

SR 277 heads east as a two-lane undivided road, leaving the town limits just west of a diamond interchange with Interstate 81.

SR 277 reaches its eastern terminus immediately to the east of the Frederick–Clarke county line at an intersection with US 522 and US 340.

At the east end, it will tie into current SR 277 about 1⁄2 mile (0.80 km) west of Double Tollgate.