PA 403 begins at an intersection with US 30 in Quemahoning Township, Somerset County, heading northeast on two-lane undivided Triple S Road.

[2][3] The road turns north into the borough of Benson and becomes Border Street, heading through more woods before entering residential areas.

The road curves north into more wooded areas with some residential and commercial development, turning northwest and passing through Tire Hill.

Here, PA 403 turns north and passes through residential neighborhoods as an undivided road, curving to the northwest past more homes with some businesses.

The road turns north and widens to four lanes, crossing the Jim Mayer Riverswalk Trail before heading across the Stonycreek River again and passing west of Greater Johnstown High School.

The road continues into dense forests as Cramer Pike, running northeast of the Conemaugh River and the Norfolk Southern line.

The road leaves the Gallitzin State Forest and heads north away from the Conemaugh River, passing through more wooded areas with some homes and intersecting the northern terminus of PA 711 in Cramer.

Past here, PA 403 turns northeast through more rural areas and passes through Virginia, crossing the Blacklick Creek into Buffington Township.

[2][5] The road continues northwest and winds through wooded areas with a few residences, running to the southwest of North Branch Two Lick Creek.

The road heads into woodland and becomes unnamed as it crosses back into Cherryhill Township and runs to the west of a R.J. Corman Railroad line.

Here, PA 403 heads into a mix of farmland and woods with some homes, passing through Dixonville and turning northwest, entering Rayne Township.

Farther northwest, the road crosses into East Mahoning Township and becomes South Manor Street, soon heading into the borough of Marion Center.