Schell first ran for mayor in 1977, but lost to Charles Royer. He then turned to real estate development, and finally won public office as a Port of Seattle commissioner in 1989, becoming commission president in 1995. He was also acting dean of the University of Washington College of Architecture and Urban Planning from 1992 to 1995.
Schell was mayor during the infamous WTO Meeting of 1999. The conclusion by many in Seattle was that the WTO convention was not worth hosting due to the economic damage and lasting image problems it caused. Controversy over the city's lack of preparation and response to the protests resulted in the resignation of Seattle police chief Norm Stamper.
In addition, Schell was mayor during a particularly violent Mardi Gras celebration in 2001 , which left 20 year old Kristopher Kime fatally injured. Arguably, both the WTO meeting and the Mardi Gras violence played a role in Schell's stunning loss to Greg Nickels and Mark Sidran in the 2001 mayoral primary election-- the first time in over 60 years a Seattle mayor had failed to survive a primary election. During the campaign, he was assaulted and seriously injured by fringe mayoral candidate James Garrett (a.k.a. Omari Tahir-Garrett). Garrett was later convicted of second-degree assault and sentenced to 21 months in prison.