Mark J. O'Brien

Attorney Mark J. O’Brien is a nationally recognized federal criminal defense attorney with nearly thirty years of experience in criminal courts all throughout the country. After beginning his professional career as a Miami, Florida prosecutor in the late 1990’s, Mr. O’Brien organized his own law firm in 2002 based upon the professional lessons he learned to that point in his life with the goal defending those accused of federal and state crimes with a mix of old school values and new school ideas. He is the firm’s managing partner.

During his first decade in private practice from 2002 to 2012, Mr. O’Brien defended individuals and corporations charged with federal crimes throughout federal criminal courts in Florida. From 2012 to the present, Mr. O’Brien has accepted the defense of clients charged in federal criminal courts throughout the entire country, in addition to his previously established federal criminal defense practice in all federal courts in Florida. Case after case, success after success, in federal court after federal court, all throughout the country, has resulted in a growing legacy. To put it simply, Mr. O’Brien wins and, as a result, he is a lawyer in demand.

Mr. O’Brien is a licensed member of the Bar of the State of Florida (1998), the Bar of the Commonwealth of Massachusetts (1998), and the Bar of the State of Montana (2023). He has practiced federal criminal defense as a member or a pro hac vice member of the following federal appellate and district courts:

• Supreme Court of the United States of America
• United States Court of Appeals for the First Circuit
• United States Court of Appeals for the Second Circuit
• United States Court of Appeals for the Ninth Circuit
• United States Court of Appeals for the Eleventh Circuit
• United States District Court for the Northern District of Alabama
• United States District Court for Alaska
• United States District Court for the Eastern District of Arkansas
• United States District Court for the Central District of California
• United States District Court for the Southern District of California
• United States District Court for Connecticut
• United States District Court for the Southern District of Florida
• United States District Court for the Middle District of Florida
• United States District Court for the Northern District of Florida
• United States District Court for the Southern District of Georgia
• United States District Court for the Middle District of Georgia
• United States District Court for the Northern District of Georgia
• United States District Court for the Southern District of Illinois
• United States District Court for the Southern District of Indiana
• United States District Court for Kansas
• United States District Court for the Eastern District of Kentucky
• United States District Court for Massachusetts
• United States District Court for the Eastern District of Michigan
• United States District Court for the Western District of Michigan
• United States District Court for the Northern District of Mississippi
• United States District Court for the Southern District of Mississippi
• United States District Court for the Western District of Missouri
• United States District Court for Montana
• United States District Court for the Southern District of New York
• United States District Court for the Northern District of New York
• United States District Court for the Western District of New York
• United States District Court for North Dakota
• United States District Court for Northern District of Oklahoma
• United States District Court for Rhode Island
• United States District Court for the Middle District of Tennessee
• United States District Court for the Eastern District of Texas
• United States District Court for the Western District of Texas
• United States District Court for the Northern District of Texas
• United States District Court for the Eastern District of Virginia
• United States District Court for the Eastern District of Washington
• United States District Court for the Western District of Washington
• United States District Court for the Southern District of West Virginia

Mr. O’Brien handles all federal criminal areas of practice, including but not limited to: Tax Fraud, Mail Fraud, Wire Fraud, Bank Fraud, Mortgage Fraud, Securities Fraud, Medicare Fraud, Health Care Fraud, Bribery, IRS Issues, Embezzlement, Insider Trading, Ponzi Schemes, Money Laundering, Sarbanes Oxley, Conspiracy to Commit a Federal White-Collar Crime, and all other Federal White Collar Crimes. Mr. O’Brien also handles Child Pornography Possession Offenses, Child Pornography Production Offenses, Child Pornography Transportation Offenses, Child Pornography Distribution Offenses, Child Pornography Receipt Offenses, Sex Trafficking Offenses, Conspiracy to Commit a Federal Sex Crime, and all other Federal Sex Crime Offenses. Mr. O’Brien also represents those charged with Drug Crimes, Gun Crimes, Conspiracy to Commit Drug and Gun Crimes, and all other General Federal Criminal Defense matters. He also handles Federal Grand Jury Investigations and Pre-File Criminal Investigations, including but not limited to Targets of a Federal Grand Jury Investigation, Subjects of a Federal Grand Jury Investigation, Witnesses of a Federal Grand Jury Investigation, and SEC, FBI, HSI, DEA, ATF, CIA, and NSI Investigations. The bottom line is if you are charged or being investigated for a federal crime, Mr. O’Brien will defend you.

Mr. O’Brien realized early on in his career that the people best positioned to defend a federal defendant are those individuals who once investigated and prosecuted federal defendants. It is important to stay one step ahead of the prosecution and their investigators and what better way to accomplish this goal than by hiring people who once did it? 

Mr. O’Brien’s federal criminal defense team includes a former United States Marine Intelligence Officer and a retired United States Drug Enforcement Administration (DEA) federal special agent. This team member has participated in all aspects of narco-trafficking law enforcement, including surveillance operations, wiretap operations, and arrest operations at the state and federal level. While a federal agent, he managed macro and micro narco-trafficking, money laundering, and weapons investigations at the state, national, and worldwide level. Over his career, he participated in world deployments, wherein he advised foreign nationals on the investigation of narco-traffickers, money launderers, and weapons distributors. He finished his career in the State of Florida, wherein he retired after twenty-five years with the DEA as a Group Supervisor. He understands how federal, state, and local law enforcement agencies and prosecutors operate nationwide.

Mr. O’Brien’s federal criminal defense team also includes a retired Internal Revenue Service, Criminal Investigations Division, (IRS CID) federal special agent, who is also a certified fraud examiner and a forensic accountant. This team member provides invaluable knowledge and expertise in all the firm’s white-collar fraud and money laundering cases. While he was with the IRS CID, he was a special agent, group manager, assistant chief and executive officer in New York City, Denver, and Philadelphia. While a special agent, he investigated and prosecuted drug cartels and organized crime members such as the New York, New England, and Philadelphia Mafia, Frank Lucas (later played by Denzel Washington in the movie about his life American Gangster), and Nicki Barnes.

Mr. O’Brien’s federal criminal defense team also includes a former Senior Supervisory United States Federal Probation Officer who served the federal judges for over twenty-five years. He has a wide-ranging background related to the United States Sentencing Guidelines and criminal statutory penalties. Over the course of his career, he prepared and analyzed nearly a thousand presentence investigation reports for accuracy and completeness (including those prepared by subordinate probation officers). As a member of the law firm, and no other, he uses the knowledge and expertise he gained during his federal government career to assist firm clients in the pre-plea, pre-sentencing, and post-sentencing phases of their federal criminal cases. 

Mr. O’Brien grew up and attended college in New York, attended law school near Philadelphia, and started his career as a prosecutor in Miami. As a result, there is almost nothing Mr. O’Brien has not seen, done, or dealt with in or out of a criminal courtroom over the course of his career. New York raised, Philly tough, and Miami tested, Mr. O’Brien brings nearly thirty years of criminal court experience to those accused of crimes in federal criminal courts throughout Florida, Massachusetts, and now the entire nation. Mr. O’Brien has the resources, both in his team and in his experience and his training, to tackle your federal criminal case and accomplish the only objective that matters: Win.

Thus, if you are being investigated and/or prosecuted by federal agents and/or federal prosecutors and are need of a federal criminal defense attorney – and a federal criminal defense team – anywhere in the United States of America, all Mr. O’Brien needs is a Wi-Fi Password and a plane to defend you.