The City Planning Commission was created in 1924 to prepare plans and gather data for urban planning and the physical development of the City, to advise City Council on current problems and long range planning, and to participate in administration and revision of the City's Zoning Ordinance. A Zoning Commission was created in 1920 to develop the City's first Zoning Code which was adopted in 1923.

The Planning Commission initially was comprised of 25 members, but in 1930, membership nine. Prior to 1946, funding for the Commission cam from the Engineering Department. A City Charter amendment in 1946 created and independent nine-member commission with fiscal autonomy. The Commission was given authority to hire employees as needed to carry out its planning and advisory functions. A Director of Planning was appointed in 1948 and, subsequently, work began on creation of the City's first Comprehensive Plan. The Comprehensive Plan was adopted in 1957. The Planning Commission also administered the Board of Adjustment which was created with adoption of the Comprehensive Plan.

The Planning Commission, along with the Urban Renewal Program, was absorbed by the Department of Community Development when the latter was established in 1969. In 1992, DCD was abolished and the Planning Commission became a self-contained entity. As an independent body, it advises Mayor, City Council, and City departments on planning policies and physical development plans and projects. It has 15 members who are Seattle residents and includes an engineer or architect, urban planner, ethnic minority members, and citizens active in neighborhood affairs.

John Spaeth was appointed as the full time director of planning in 1948. Spaeth hired a planning staff and worked with business leaders, neighborhood organizations, and civic groups to garner support for the idea of a Comprehensive Plan. In developing the Plan, Spaeth and his staff created the City's first neighborhood plans for those post-World War II areas that were expanding at a rapid rate. He also focused on planning for the Central Business District. Following development of the Comprehensive Plan, the City adopted a new Zoning Code based on the Plan. Spaeth retired from City service in 1971.