Johnson beat incumbent Commissioner Richard Boykin in the Democratic primary election in March 2018. He won the general election unopposed and was reelected in 2022.
In the 2023 Chicago mayoral election, he won the second-most votes in the first round on February 28 with 21.6%, while Paul Vallas won 33% of first-round votes. In the April 4, 2023 runoff election, Johnson beat Vallas and was elected the 57th Mayor of Chicago.[5][6]
In 1998, he married Stacie Rencher. They have three children. He lives in the Austin neighborhood of Chicago.