Summersville is located off U.S. 19 at the intersection of State Routes 39 and 41, at an elevation of 1,894 feet. It is the county seat of Nicholas County.

Nicholas County was founded in 1818, and land at present Summersville was donated by John Hamilton as a site for the county seat. The town was established about 1820 and incorporated in 1860. Summersville was named for Judge Lewis Summers, who introduced the legislation in the Virginia General Assembly to create Nicholas County. The first courthouse, a two-story frame structure, served until the present stone courthouse was completed in 1898.

Summersville was located on the Weston & Gauley Bridge Turnpike, an important thoroughfare during the Civil War and heavily used by troops of both sides. Early in the war, battles were fought nearby, at Keslers Cross Lanes and Carnifex Ferry. Summersville was occupied by both Northern and Southern troops late in the war, and suffered a devastating fire that destroyed much of the town. Summersville also was the site of a daring escape by Confederate spy Nancy Hart. The battlefields, as well as Summersville Lake State Park and nearby Gauley River National Recreation Area, now attract tourists to the area, especially during the warm months.

In 1914, the first Nicholas County High School opened in Summersville. The Renaissance Revival building was designed by noted Charleston architect H. Rus Warne. From 1915 to 1930, it also served as a normal school for training teachers. The high school remained open until a new one was built in 1978. The original building, listed in the National Register of Historic Places, is now the Old Main Arts & Heritage Center.

The completion of the New River Gorge Bridge and Appalachian Corridor L (U.S. 19) in the 1970s brought heavy traffic through Summersville and spawned much commercial development along the four-lane highway. Corridor L is a popular shortcut from Interstate 79 to the West Virginia Turnpike, bringing many Florida-bound Pennsylvanians, New Yorkers, and Canadians to Summersville motels and restaurants.

Summersville’s population has grown significantly since Corridor L’s completion, from 2,429 in 1970 to 3,459 in 2020, a 42.4 percent increase. As of 2020, Summersville was West Virginia’s 37th largest city.