In the U.S. state of New Hampshire, U.S. Route 1 is a major north–south state highway through Hampton and Portsmouth. It lies between Interstate 95 and New Hampshire Route 1A.

The Memorial Bridge, which formerly carried US 1 over the Piscataqua River between New Hampshire and Maine, was closed to motorists in July 2011 due to numerous safety and structural concerns. This was a permanent closure following two instances in 2009 and 2010 when the bridge was closed for emergency repairs. The bridge was, however, left open to pedestrians and bicyclists, as it was the only of the three river bridges allowing for these methods of travel. Just over five months later, the bridge was closed to all travelers and the middle lift section was removed, leaving a gap in US 1. A new bridge is being constructed over the existing piers and is scheduled to open in 2013.

In the interim, access to US 1 on each side of the gap may be facilitated by the Sarah Mildred Long Bridge, which carries US 1 Bypass, or the Piscataqua River Bridge which carries I-95. The New Hampshire Department of Transportation is also operating hourly shuttle service between Portsmouth and Kittery while the new bridge is constructed.

US 1 follows the historic Lafayette Road through New Hampshire, named after the Marquis de Lafayette, who passed over the road in 1825.

New Hampshire Route 1A is an 18.32-mile (29.48 km) long state highway located in southeast New Hampshire. The route runs along the Atlantic coastline from the Massachusetts border north to Rye, then turns toward downtown Portsmouth. The southern terminus is at the Massachusetts state line in Seabrook at the junction with Massachusetts' Route 1A. The northern terminus is at the junction with U.S. Route 1 in Portsmouth. For the length of the road’s run along the shore, its local name is Ocean Boulevard. In Portsmouth, it is known as Miller Avenue and Sagamore Avenue.

New Hampshire Route 1B (abbreviated NH 1B) is a 4.89-mile (7.87 km) long state highway in southeast New Hampshire.

The southern terminus is at New Hampshire Route 1A in Portsmouth, near the city's southeastern boundary. The road loops around over Great Island in the Piscataqua River through New Castle and then back into Portsmouth. The northern terminus is at the junction with U.S. Route 1 near the Maine state line.