In 1921, the highway from Ottawa to Arnprior was extended to Pembroke via Renfrew, Cobden and Beachburg. By 1925, the entire route from the Quebec border through Ottawa and up to Pembroke became known as Highway 17.
In Ottawa, the original routing of Highway 17 was Carling Avenue, Richmond Rd, Wellington Street, and Rideau Street to Montreal Road. East of Ottawa, The original routing of Highway 17 followed what is now Montreal Road, and the Old Montreal Road eastward out of Ottawa; And from Ottawa east through Rockland (Laurier Street) to Hawkesbury (Eliza Street, Front Road and Main Street); and then following the shore of the Ottawa River between Hawkesbury and Pointe-Fortune, located on the Quebec border
During the 1940s, several deficiencies were noted on the original route of Highway 17 between the Quebec border and Ottawa, which required some widening, straightening, and flattening of the original route. At the time, the planning and construction was already underway for the new dam on the Ottawa River, which would flood part of the route. By the end of 1953, about 40 km of Highway 17 had been relocated and the completed length of the relocated Highway 17 was 61.5 km. in 1954, a Plantagenet Bypass was also completed
Highway 17 largely follows its original routing, other than the portion of this original highway was flooded (along with the Long Sault Rapids) when the Carillon Generating Station in 1964 raised the water level of the Ottawa River 18 meters (59 ft) just north of Voyageur Provincial Park and the Ontario-Quebec border.
The 1976 Summer Olympics in Montreal led to planning for a new freeway, Highway 417 to connect the Queensway east of Ottawa to Autoroute 40 into Montreal. The meandering Highway 17 along the shore of the Ottawa River was accident prone and had a low traffic capacity. Construction was accelerated to handle anticipated high volume of traffic between Ottawa and Montreal during the games. Construction was begun in 1969, and the new route opened to traffic in late 1975. The old two-lane route was re-designated 17A.