Vermont Route 18 begins at the New Hampshire state line between Littleton and Waterford.

VT 18 then continues northwest running closely parallel to I-93 on its west side for roughly 7 miles (11 km) until Stiles Pond.

Soon after junction with I-93, which is the only numbered exit on that route in Vermont, VT 18 and US 2 Truck end at U.S. Route 2 about 0.25 miles (0.40 km) past the St. Johnsbury town line.

[3] Vermont Route 18 was originally part of the Theodore Roosevelt International Highway, a transcontinental auto trail organized in 1919 running from Portland, Oregon to Portland, Maine via Ontario.

The previous alignment from Montpelier to Wells River was designated as part of newly established U.S. Route 302,[citation needed] and the overlap with U.S. Route 5 was eliminated.