Dennis P. O'Brien, Esq.

Mr. O’Brien began his career as an Assistant District Attorney with the Nassau County District Attorney’s Office. Serving as a prosecutor from 2002 until 2006, Mr. O’Brien handled a wide array of criminal matters including the most serious violent felonies. Upon leaving the District Attorney’s Office, Mr. O’Brien managed a criminal defense firm in Garden City and Huntington for fourteen years. During that time, he amassed significant litigation experience. This experience includes grand jury, litigated motions, pre-trial hearings, and trying cases to verdict. His litigation practice also included varied administrative proceedings such as refusal and fatality hearings and the corresponding departmental appeals procedures, firearms licensing, and New York Police Department administrative reviews.

In 2016 Mr. O’Brien was recognized by the members of the Fraternal Order of Court Officers (FOCO), which is an organization of New York State Court Officers and Court Clerks, with the Amicus Fraternitas Award, which is awarded to a member of the legal community based on his professionalism, dedication and integrity.

He was elected and served as a member of the Board of Directors of the Criminal Courts Bar Association of Nassau County from 2008-2016. During his time on the Board of Directors, Mr. O’Brien chaired the Legal Action Committee. In this capacity, he authored several Amicus Curiae briefs on behalf of the Association. In 2015, he was elected President of the organization and dutifully served in this office, frequently participating in meetings with senior representatives of the Office of the District Attorney and the Supervising and Administrative Judges of the Courts of Nassau County. In addition to his service with the Criminal Courts Bar Association, he has also served as Vice Chair and Chair of the Criminal Courts Law and Procedure Committee of the Nassau County Bar Association.

Mr. O’Brien is an Adjunct Professor at St. John’s University and has been teaching courses on the law for the past eighteen years. He also continues to present his academic writing at colloquia and conferences throughout the country.

Mr. O’Brien received his J.D. from Brooklyn Law School, M.A. from St. John’s University, and B.A. from St. John’s University. He is also a graduate of Chaminade High School. Mr. O’Brien is a member of the Nassau, Suffolk and New York State Bar Associations, the Criminal Courts Bar Association of Nassau County, and the National Association of Criminal Defense Lawyers, and is admitted to practice law in New York State and the Eastern and Southern Districts of New York.