The Mayor is the chief executive officer of the City with responsibilities for appointing executive department heads, directing and controlling all subordinate officers and agencies, preparing and executing the City budget, ensuring that the laws of the City are enforced, and maintaining the peace and order in the City. The legal roles and responsibilities of the Mayor are prescribed by the City Charter, state statutes, and municipal ordinances. A candidate for the position must be a citizen of the United States, a qualified elector of the State of Washington, and a registered voter of the City of Seattle at the time of filing his/her declaration of candidacy.

Seattle was incorporated by an act of the Territorial Legislature on December 2, 1869, and the City's first mayor, Henry A. Atkins, was appointed by the Legislature pending the first City election scheduled for July 1870. The City Charter, granted by the Legislature, set the Mayor's term of office at one year. Under this first Charter, the Mayor served as ex-officio President of the Common Council. A Charter amendment in 1875 gave the Mayor a vote on Council, but that provision was amended in 1886 to provide for a tie-breaking vote only.

The City's first Freeholders' Charter (1890) completely separated the Executive and Legislative branches and changed the term of office for the Mayor to two years. Through the first decade of the 20th century, elected offices in Seattle were partisan. A Charter Amendment passed by the voters on March 8, 1910, established non-partisan nominations and elections for all City elective offices. A new Freeholders Charter in 1946 changed the term of the Mayor to four years.