Criminal Defense Lawyers
Clay County and Northeast Florida
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Mark Sieron

A North Florida Criminal Defense Attorney Focused on Results

Criminal Defense Attorney Mark Sieron

Florida criminal defense lawyer Mark Sieron has a reputation as a top attorney in the Clay County and Jacksonville area who delivers results. His hard work and passion for his profession are reasons why he has consistently earned the respect and admiration of clients, colleagues, and judges throughout North Florida. For over two decades he has been honored with the "AV-Preeminent 5-star" rating, the highest possible rating by Martindale Hubbell, the nation's oldest and most respected attorney rating service. Throughout his legal career, Mark has received numerous awards and honors from respected legal organizations.

Mark graduated with honors from the University of Florida's College of Journalism & Communications in 1981 and College of Law in 1984. He was admitted to The Florida Bar in 1985 and has practiced law for over thirty years, primarily in Clay and Duval counties.

Mark began his career as a trial attorney while still in law school, successfully taking several cases to trial when he was a certified intern in Jacksonville's State Attorney's Office.  After his internship, State Attorney Ed Austin hired Mark as a prosecutor in Florida's Fourth Judicial Circuit (Clay, Duval, and Nassau counties). As an Assistant State Attorney, Mark prosecuted and tried cases ranging from DUI to murder in Duval and Clay counties.

After several successful years as a prosecutor, Mark accepted a position as a trial lawyer with Kopelousos, Head, Smith, Townsend & Metcalf, P.A., Clay County's largest and most respected law firm.  Five years later, he and Bob Aguilar became partners in the firm, which continues to this day as Aguilar & Sieron, P.A.  Mark has specialized in criminal defense for more than 25 years, proudly defending people from all walks of life. He has always held strong beliefs in the rights of all who are accused to receive the fairest treatment possible in our criminal justice system.


Mark was born at Eglin Air Force Base, Florida and grew up in a military family, living in Florida, Utah and Germany. After his father's retirement from the Air Force, the family settled in Crestview, a small town in Florida's panhandle. At Crestview Senior High, Mark was elected president of his senior class, captain of the football team, and captain of the track and field team. In 2013, he was honored by his induction into the Crestview High School Athletic Hall of Fame. At the University of Florida, Mark was regularly named to the Dean's List, while earning varsity letters on the track and field team and working for the school newspaper.

Mark met his future wife Robyn at UF, and they were married while he was in law school. Robyn is a former TV anchor/reporter who now operates her own broadcast production company. They've been married over 33 years and have two children. In 2010, their son Grant graduated from Princeton University, where he played football for four years.  He now works in New York City. In 2014, their daughter Kendall graduated magna cum laude from Florida State University, where she was a member of the school's swim team. She now works in Atlanta.

Honors and Awards

  • Rated an outstanding lawyer by Super Lawyers 
  • Rated AV-Preeminent by Martindale-Hubbell for over 20 years
  • Named Top 100 Trial Lawyers by National Trial Lawyers Association
  • Named Top 1% of lawyers by National Association of Distinguished Counsel
  • Named multiple times as one of Jacksonville's Best Criminal Defense Lawyers by Jacksonville 904 Magazine


  • The Florida Bar, 1985 - Present
  • U.S. District Court, Middle District of Florida, 1987 - Present

Professional Activities

  • Three-time President, Clay County Bar Association
  • Jacksonville Bar Association
  • National Association of Criminal Defense Lawyers
  • Florida Association of Criminal Defense Layers
  • Northeast Florida Association of Criminal Defense Lawyers
  • Criminal Law Section of the Florida Bar
  • Lecturer, Clay County Bar Association
  • Lecturer, Florida Justice Association

Areas of Practice

  • DUI Charges
  • Drug Charges
  • Juvenile Crimes
  • Violent Crimes
  • Firearms Charges
  • Domestic Violence
  • Pre-Arrest Investigations
  • Probation Violations
  • Theft Crimes
  • Sex Crimes

Community Service

  • President and Founder, Jacksonville Basketball League (2001-2010)
  • President, San Jose Athletic Association (2001-2004)
  • Former Vice-Chairman, Jacksonville Sports Entertainment Commission
  • Board member, Children's Haven (for abused children)
  • Board Member, Lighthouse Learning Center
  • Vice-President, Jacksonville Gator Club
  • Member, The F Club (for University of Florida varsity letter winners)
  • Youth league coach for baseball, basketball, and football (1995-2004)
  • Varsity Track & Field Coach, The Bolles School (2007-present)
  • Member, Holy Family Catholic Church