The City Planning Commission was created by ordinance in 1924 and was first included in the City Charter in 1946. The Commission's role was to prepare plans and gather data for the development of the City, to advise City Council on current problems and long range planning, and to participate in administration of the City's Zoning Ordinance. It was provided with the authority to hire as needed to carry out its planning and advisory functions. However, the Planning Commission's decisions needed to be passed by ordinance before they became effective.

Between 1924 and 1974, the Commission's membership was changed periodically by ordinance. It varied in size from 9 to 25 members. The composition of the Commission also varied but always consisted of a percentage of the following: Mayoral appointees, ex-officio members from various government departments, as well as representatives elected by various government agencies.

With the creation of the Department of Community Development in 1969, the Commission became a part of the Department of Community Development. For the purpose of having a more broad-based membership, in 1974 the Commission membership was changed to be comprised of 15 Seattle citizens, appointed by the Mayor and approved by City Council. If at all possible, the citizens would come from different neighborhoods and a variety of disciplines would be represented.

Due to reorganizations in city government, the Planning Commission became a part of the Office of Policy Planning in 1974 then was returned to the Department of Community Development in 1979. In 1980, an independent office of the Planning Commission was established. The Planning Commission would no longer review site-specific land use applications and permits. Its city planning functions were transferred to the Department of Community Development.