It is a primary thoroughfare through western Pennsylvania and West Virginia and makes up part of an important corridor to Buffalo, New York, and the Canada–United States border.

Major metropolitan areas connected by I-79 include Charleston and Morgantown in West Virginia and Greater Pittsburgh and Erie in Pennsylvania.

In the hillier areas, this flatness is achieved by curving around hills, along ridges, and in or partway up river valleys.

I-79 begins at a modified full Y interchange with I-77 along the northwest bank of the Elk River just northeast of Charleston.

I-79 is carried over the Ohio River by the Neville Island Bridge, approximately eight miles (13 km) northwest of Pittsburgh.

Around milemarker 100 on the northbound side are two ghost ramps that were specifically built for the Boy Scouts of America in order to have access to Moraine State Park without having to travel on US 422 for the 1973 and 1977 National Scout Jamborees, which were held at Moraine.

In September 1955, two short urban portions were designated:[9][10] The number 79 was assigned in 1958,[12] and an extension south along I-70 to Washington and beyond to Charleston was approved on October 18, 1961.

(The part of US 19 from Sutton south to I-77 at Beckley, West Virginia, has since been four-laned as Corridor L of the Appalachian Development Highway System.)

On December 21, 1967, the first section of I-79 in West Virginia, between exits 125 (Saltwell Road) and 132 (South Fairmont), opened to traffic.

[14] This five-mile (8.0 km) section bypassed part of West Virginia Route 73 (WV 73) between Bridgeport and Fairmont.

Another five miles (8.0 km) opened in July 1968, extending the highway on a bypass of downtown Fairmont to exit 137 (East Park Avenue).

[15] It was further extended 9.5 miles (15.3 km) toward Morgantown on October 15, 1970, bypassing more of WV 73 to exit 146 (Goshen Road) south of that city.

[21] A further extension of six miles (9.7 km), including the Uffington Bridge over the Monongahela River southwest of Morgantown, was opened on August 30, 1973, leading north to exit 155 (Star City).

[40] In 1984, the route was extended about one mile (1.6 km) further to the north, with the opening of a new segment between US 20 and PA 5 in Erie.

In 2025, WVDOT expects to compete a six-lane widening between Harrison County and the Pennsylvania state line.