Sean O’Callaghan

Sean O’Callaghan

phone (312) 600-5588


Sean O’Callaghan is a partner at O’Mara & O’Callaghan, where his practice focuses on general business counseling and litigation. Sean has guided multimillion dollar companies through mergers and acquisitions as well as advised small startups regarding formation and partnership matters. When necessary, Sean has successfully represented his clients in state court, federal court, mediations, and arbitrations.

While Sean has represented companies and clients engaged in a wide variety of business fields, he does have a concentration in the financial services, particularly those in the futures and derivatives industry. To better serve those clients, Sean is presently working toward his LLM in Financial Services at Chicago-Kent College of Law, the focus of which has been on market regulation, enforcement, and litigation of securities and commodities law matters.

For the first eight years of his legal career, Sean served the people of Illinois as an Assistant State’s Attorney in the Cook County State’s Attorney’s office. After starting his career in the Appellate Division writing legal briefs, he moved up through the trial ranks prosecuting every type of criminal case from theft to murder. During his time in the trial division, Sean tried numerous cases to juries and argued hundreds of motions and bench trials.

Sean attended the University of Iowa, College of Law, where he graduated with distinction. While in law school, he was a member of the Iowa Law Review and a member of the law school’s Moot Court Board. He also clerked in the real estate practice group of Wildman Harrold (now Locke Lord) in Chicago.

He earned his bachelor’s degree from the University of San Diego, where he was a four-year recipient of the university’s Dean’s Scholarship and graduated with departmental honors in English. Between college and law school, he worked in commercial real estate leasing in San Diego.

Sean’s father is a proud Chicago Police Officer, now retired, and his mother recently retired from a career as a professor at a local university. Sean lives in Chicago with his wife and two children.

In 2017, Sean was named to the Chicago Daily Law Bulletin’s prestigious “Forty Under Forty.”


  • University of San Diego, B.A. in English, 1999
  • University of Iowa College of Law, J.D., 2005


  • Federal Bar, Northern District of Illinois
  • Federal Trial Bar, Northern District of Illinois


  • Illinois State Bar Association
  • Chicago Bar Association