The Seaway Trail was conceived in 1978 by William E. Tyson, executive director of the St. Lawrence-Eastern Ontario Commission, whose initial work led to the New York State Legislature designating the trail in 1980. It was originally an byway extending from the Thousand Islands Bridge to the Seaway International Bridge by way of a series of highways paralleling the Saint Lawrence Seaway. Signage for the trail was erected shortly afterward by the New York State Department of Transportation. It received its first designation in 1983 when it was recognized as a National Recreation Trail by the National Park Service. The trail was extended southwestward around the edge of Lake Ontario to Niagara Falls in 1984 and along the shores of the Niagara River and Lake Erie to the Pennsylvania state line in 1986, completing the byway's modern alignment within New York. It was later designated as a New York State Scenic Byway.