The city's law office said Thursday that the resignation will become effective mid-February.
Patton has been with Mayor Rahm Emanuel's administration since May 2011. A statement from the mayor's office praised Patton for his work to resolve the Shakman lawsuit, reparations for Jon Burge victims and most recently, supporting the DOJ investigation into the Chicago Police Department.
Emanuel's office announced Thursday that Patton will be replaced by Edward N. Siskel. Siskel is currently a partner at the law firm of WilmerHale in Washington D.C.