Judge Pat O'Brien was born and raised in Chicago, where he attended St. Ignatius High School. Upon receiving his B.A. from the University of Notre Dame, Judge O'Brien returned home to attend DePaul University College of Law. O'Brien became a licensed attorney in the State of Illinois in 1975 and has practiced continually since, working in both the public and private sector.
Judge O'Brien has twice worked in the Cook County State's Attorney Office, handling high-profile cases representing the State of Illinois. As a result of his dedication to serving justice, O'Brien received appointments to high-level leadership positions in the Felony Review Unit as Felony Trial Supervisor, Bureau Chief of the Criminal Division, and finally, Chief Deputy — accountable for over 700 Assistant State's Attorneys handling criminal cases in Cook County.
O'Brien also served as an Assistant Illinois Attorney General, where he assisted State's Attorney's Offices across the State of Illinois with major criminal cases, often working closely with the elected State's Attorneys in each county.
Judge Pat O'Brien's impressive record as a public attorney served him well when in 2006, O'Brien was elected as a Judge of the Cook County Circuit Court, where he presided in both criminal and civil courtrooms for eight years, before returning to private practice.
Given Judge O'Brien's extensive prosecutorial and judicial experience, O'Brien's private practice has concentrated on criminal law, where he has provided fair representation for defendants. During this time, Judge Pat O'Brien has also been honored to be appointed a Hearing Officer for the City of Chicago Liquor Commission and as Attorney for the Police Board.