Highway 48 was first designated in 1937 to connect Port Bolster with Highway 12 in Beaverton. It was extended south to meet with Highway 401 in the 1950s in anticipation of a planned freeway connection around the eastern shore of Lake Simcoe that ultimately became Highway 404. In the mid-1970s, Highway 48 assumed a portion of the route of Highway 46 in Victoria Country, now the city of Kawartha Lakes, extending the route to Highway 35 in Coboconk. Between then and 1998, the route was . However, on January 1, 1998 the province transferred the responsibility of maintaining the southern and northern sections to the regional governments that those sections lie within.