SR 900 was created in the 1964 state highway renumbering, but the corridor had been part of the state highway system since 1909. It was originally a section of the Sunset Highway, the main cross-state route between Seattle and Spokane and was designated as U.S. Route 10 (US 10) in 1926. After the opening of the Lake Washington Floating Bridge, US 10 was moved to a new highway and the former alignment through Renton became an alternate route and a branch of Primary State Highway 2 that was replaced by SR 900. The highway originally terminated at an interchange with I-90 in Seattle's Rainier Valley, but was truncated in 1991.