Schell died Sunday morning at a Seattle hospital surrounded by family, according to Mayor Ed Murray's office.
"Paul will be greatly missed. He was truly committed to the people of Seattle, working to improve the city both as an elected official and private citizen. He was dedicated to the lives of the people of this city, evidenced by his countless contributions and the legacy he built here," Murray said in a statement.
Murray described Schell as one of the city's great "builders." Under Schell, Seattle approved funding to build the world-renowned downtown library. He also led efforts for the first parks levy and played a key role in constructing the Olympic Sculpture Park and the City Hall. He championed the arts and began a massive effort to draft plans for all 37 neighborhoods.
Schell, the city's 50th mayor, served one term as mayor from 1998 to 2002 before losing a re-election bid to Greg Nickels.
His one term was marred with street clashes. The city's response to the WTO protests was heavily criticized and led to the resignation of the police Chief Norm Stamper. The city was also sued by dozens of the protesters, eventually settling. In 2001, a riot broke out during Mardi Gras in Seattle's Pioneer Square, leaving one man dead and scores assaulted.
Schell is survived by Pam, his wife of 51 years, and his daughter, Jamie.