The route runs along the Atlantic coastline from the Massachusetts border north to Rye, then turns toward downtown Portsmouth.

NH 1A continues as a four-lane divided highway running directly next to the coastline beaches.

The road continues another mile or so, crossing into North Hampton, and meets the eastern end of NH 111.

The road turns back north at the intersection known as Foyes Corner and enters the Portsmouth city limits, passing the southern end of NH 1B (a connector to New Castle).

NH 1A continues towards downtown Portsmouth, where it ends at the intersection of Miller Avenue and Middle Street (US 1).