PARTNER
DENNIS 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. After leaving the District Attorney's Office, Mr. O'Brien was in private practice for fourteen years before joining Frazer & Feldman. During his time in private practice, Mr. O'Brien developed significant trial experience. In addition, he also served as a hearing officer for numerous student discipline matters.
Since joining the firm in 2020, Mr. O'Brien has focused on all aspects of employee and student discipline and general litigation and became a Partner of the firm in 2025. He has handled multiple complex proceedings pursuant to Education Law 3020(a), relating to the discipline of tenured teachers. Mr. O'Brien has also prosecuted many matters pursuant to Civil Service Law § 75, as well as litigated public sector union arbitrations. In addition, Mr. O'Brien routinely advises clients on matters related to student discipline, and regularly handles student discipline hearings, pursuant to Education Law 3214.
Mr. O'Brien has also served as lead counsel in federal and state litigation. He has handled civil actions in both state and federal court, proceedings for temporary restraining orders in both state and federal court, and proceedings pursuant to Article 78 of the CPLR. Mr. O'Brien has headed investigations into violations of Title IX, Board harassment policies, as well as general employee misconduct. In addition, Mr. O'Brien has also represented and defended Districts in investigations by state agencies into their policies and procedures. He regularly attends Board Meetings, as general counsel, for multiple school districts. Mr. O'Brien has also served as lead negotiator for multiple collective bargaining agreements. Mr. O'Brien has served as a panelist/lecturer at many school law conferences. His presentations have centered on student and employee discipline.
Mr. O'Brien is an Adjunct Professor at St. John's University and has been teaching courses on the law for the past twenty-five years. He also continues to present his academic writing at colloquia and conferences throughout the country.