The portion of road between Weissport and Lehigh Gap was originally designated as part of US 309 when the U.S. Highway System in 1926. In 1927, PA 45 was designated and ran between Weissport and Easton, running concurrent with US 309 before turning south from the Lehigh Gap along the Lehigh River to Northampton and then east to Bath. The route was moved to a more direct alignment between Lehigh Gap and Bath a year later. PA 45 originally had its eastern terminus in Easton at US 22 at the intersection of 13th and Northampton streets in Easton. The route was extended east along Northampton Street to the Northampton Street Bridge over the Delaware River following the rerouting of US 22 to a freeway in 1955. In the 1950s, PA 29 replaced the US 309 designation concurrent with PA 45 between Weissport and Lehigh Gap. In 1961, PA 29/PA 45 was upgraded to a divided highway, with the portion between Bowmanstown and Lehigh Gap built as a freeway. PA 248 was designated to its current alignment on May 9, 1966, replacing the PA 29 and PA 45 designations.