Sean O'Brien Law

About And Experience


At Sean O'Brien Law, loyalty is evident through relentless preparation, client communication, and an aggressive approach to litigation. A former prosecutor with extensive litigation and trial experience, he understands what it takes to win.



Mr. O'Brien has extensive experience trying cases in courtrooms throughout Chicago and Illinois in both state and federal courts. Prior to forming O'Brien & Murphy-Aguilú, Mr. O'Brien defended criminal matters ranging from traffic cases to murder charges as an Associate Attorney for one of the largest criminal defense firms in Chicago. There, Mr. O'Brien concentrated his practice on large narcotics cases.

For the first portion of his career, Mr. O'Brien served as a prosecutor in the Cook County State's Attorney's Office where he gained significant experience trying motions and trials for complex narcotics cases as a Special Prosecutor in the Narcotics Bureau.

Mr. O'Brien has tried hundreds of bench trials, jury trials, and motions.  He is an expert in narcotics, search and seizure law, traffic, appeals, forfeiture cases, and expungements.