In 1971, Sawyer was elected as an alderman of the 6th ward. He continued in the position until 1987 when the sudden death of Harold Washington created a vacancy in the position of mayor. Sawyer was elected mayor by the other members of the city council and took over from interim mayor David Duvall Orr. Sawyer's inauguration occurred in the parking lot of a closed restaurant at 4:01 AM on December 2, 1987.
While Washington's time as mayor was filled with controversy and racial hostility from white conservative and white ethnic voters (and politicians), Sawyer's tenure went much more smoothly. Sawyer managed to pass several major initiatives begun by Washington. These included placing lights in Wrigley Field, an Ethics Ordinance to prevent corruption, and one of the first human rights ordinances that protected gays and lesbians from discrimination.