He will run against incumbent Rahm Emanuel, who fired McCarthy from his position as Superintendent after the Laquan McDonald shooting.
"It's no secret that for the last several months literally thousands of Chicagoans have asked me to run for mayor," McCarthy said in a statement Friday. "I have taken those calls to heart because I know the city is badly in need of genuine leadership and real change. At some point next week I will be making my final decision and sharing that with my supporters and the citizens of Chicago."
McCarthy is expected to officially announce his candidacy next week. The election will be held in February 2019.