Mark J. Gaertner is a native of St. Louis. He graduated from Rohan Woods School, Chaminade Preparatory School, St. Louis University and St. Louis University School of Law.

After graduating from law school, he was a law clerk for the Missouri Court of Appeals. Mark then went to work for Anheuser-Busch Companies in their executive training program. While working for Anheuser-Busch, he became a member of the Office of Professional Employees International Union (OPEIU). After working for Anheuser-Busch Companies, Mark returned to private practice with Holloran Schwartz & Gaertner LLP.

Mark is a member of the St. Louis County Bar Association (Executive Board Member 2009 – Present), The Missouri Association of Trial Lawyers (Board Member 2009 – 2018, Past President 2016-2017), American Bar Association, Bar Association of Metropolitan St. Louis, The Lawyers Association of St. Louis, The American Association for Justice, and The Women Lawyers’ Association of Greater St. Louis. Mark comes from a distinguished legal family. His father is a retired Missouri Court of Appeals Judge and former Circuit Judge in St. Louis City, and his older brother is a Missouri Court of Appeals Judge and former Circuit Judge in St. Louis County.

In December 2009, Mark was honored to be introduced as a named partner in the Firm. In 2011 and 2012, Mark was recognized as a Rising Star by the Missouri and Kansas Super Lawyers. In 2013, he was selected as a Super Lawyer by the Missouri and Kansas Super Lawyers, and has been selected every year since. Since 2011, Mark has been recognized as a member of the Top 100 Trial Lawyers by the National Trial Lawyers. Mark has achieved the prestigious Martindale-Hubbell Peer Review Rating.

From 2016 – 2021, Mark served on the Board of Police Commissioners for the St. Louis County Police Department.  He was Secretary of the Board of Police Commissioners. The Board of Police Commissioners is the final authority for the control and supervision of the St. Louis County Police Department. Mark also served as a Chairperson on the St. Louis County and Municipal Police Academy.

In May 2021, Mark was sworn in as the Judge for the City of Chesterfield and the City of Clarkson Valley.  In January 2023, Mark was appointed as the Judge for the City of Ladue.  As the Judge for those cities, he is the chief judicial officer and assumes the primary responsibility for the administration of the court.

In December 2023, Mark was selected to be the Secretary and Board Member of The BackStoppers.  The BackStoppers provide financial assistance and support to the spouses and dependent children of first responders who have lost their lives or suffered a catastrophic injury in the line of duty.

In January 2024, Mark was selected to be the treasurer and Board Member of the Law Enforcement Legislative Coalition (LELO).  LELO represents law enforcement through legislation and education to improve public safety.

Mark has tried multiple cases including personal injury matters and also lectures at various legal seminars concentrating on difficult trial practices. Mark’s primary focus is personal injury, professional negligence, wrongful death, product liability, class action, minimum wage and overtime cases, motor vehicle accidents, work-related injuries and business and consumer litigation.

Mark remains active in the community through organizations such as The BackStoppers (Family Adoption Program, 2012 – present), Respond and Rescue (Board Member, 2016 – present), and Ancient Order of Hibernians.