About Benjamin Henry
Benjamin Henry Mainzer grew up studying ideas and institutions. He earned a B.A. from the University of Chicago in 2005 and later attended Vanderbilt University Law School. Those years shaped his interest in courtroom work and the mechanics of litigation.
He began his legal career in northern California. In 2009 he served as a deputy district lawyer in the Humboldt County District Lawyer's Office, where he handled day-to-day prosecutorial responsibilities and courtroom appearances. That early public-service work put him in front of juries and judges and gave him sustained experience in trial practice.
In 2011 Mainzer moved into private practice as a partner at Bragg, Mainzer & Firpo, LLP. Over the next decade he handled a steady docket of litigated matters, representing clients in filings, motions, and contested hearings. In 2020 he joined Reiner, Slaughter, Mainzer & Frankel as a partner. The firm role expanded the range of matters he took on and involved more counseling of clients across complex procedural issues.
Mainzer is admitted to practice in California and holds memberships in several federal courts. He is a member of the United States Court of Appeals for the Ninth Circuit and of the U.S. District Courts for the Northern and Central Districts of California. He also belongs to the Humboldt County Bar Association. Those admissions have allowed him to appear in both trial and appellate forums over the course of his career.
Colleagues describe Mainzer as methodical in preparing for hearings and direct in court. He blends courtroom experience from his time in the Humboldt County office with the demands of private litigation. He has managed cases from initial complaint through dispositive motion practice and through appeals in federal and state venues.
Outside the courtroom he has stayed active in bar activities at the local level and maintained ties to the northern California legal community. He returns regularly to matters that require in-court advocacy and written briefing. He currently practices at Reiner, Slaughter Mainzer & Frankel, LLP in California, where he handles trial and appellate work in state and federal courts.
