U.S. Route 4 in New Hampshire runs for 106.834 miles (171.933 km) across the central and southern part of the state, stretching from Lebanon on the Connecticut River border with Vermont southeast to Portsmouth on the eastern coast.

At this point, NH 10 joins the I-89 freeway southbound, while US 4 continues east into downtown Lebanon.

US 3 and US 4 share a short concurrency (about a mile [1.6 km]), before US 4 turns east to interchange with I-93 at Exit 17.

US 4 continues east toward the coast and crosses the tidal Bellamy River to enter Dover, then interchanges with the Spaulding Turnpike (NH 16).

US 4 joins the turnpike southbound, closely paralleling the Maine state border and crossing the Little Bay Bridge into the town of Newington before continuing into the city of Portsmouth.

Until I-89 was built in the early 1970s, this was part of the main route between the Lebanon–Hanover area and the southeastern portion of New Hampshire.

The southern terminus is in the town of Andover at NH 11, about 0.75 miles (1.21 km) southwest of its intersection with US 4.