Mary Longenbaker focuses her practice on data privacy litigation and compliance. She advises clients across a wide range of industries on compliance with U.S. privacy laws, incident response and litigation strategies.  

As a Certified Information Privacy Professional/United States (CIPP/US), Mary brings a nuanced understanding of data protection frameworks and regulatory requirements, helping clients navigate the evolving landscape of privacy compliance with confidence. Mary regularly leverages her knowledge of U.S. privacy law and experience as a litigator to assist clients during all phases of data breach litigation. She also assists with contract negotiations, privacy policy development and cross-border data transfer issues.

Mary is known for her practical, business-focused approach to legal challenges and her commitment to helping organizations harness technology while managing legal and regulatory risk.

Education

  • Vanderbilt Law School (J.D., 2016)
    • University of Notre Dame (B.A., cum laude)
      • Political Science & Mandarin Chinese

    Bar Admission

    • District of Columbia
    • Missouri

    Court Admissions

    • U.S. District Court, Eastern District of Missouri
    • U.S. District Court, Western District of Missouri
    • U.S. District Court, District of Kansas

    Professional Affiliations

    • International Association of Privacy Professionals
    • Bar Association of Metropolitan St. Louis
    • Bar Association of the District of Columbia

    Languages

    • Chinese
    Publications
    All Publications
    Can State Legislation Help Stem the Onslaught of Data Breach Lawsuits?
    Shundra Crumpton Manning and Mary Longenbaker explain how new state safe harbor laws are limiting post-breach liability for companies that follow recognized cybersecurity standards, with courts beginning to shape their impact on class actions. Read the full article in the 2026 Technology Transactions & Data Privacy Annual Report. 
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    2026 Technology Transactions & Data Privacy Report
    The Polsinelli Technology Transactions & Data Privacy team is pleased to announce the publication of its sixth annual Technology Transactions & Data Privacy Report, featuring insights into the latest trends and developments shaping today's data privacy, cybersecurity and technology landscape. This report brings together thought leadership from our attorneys, outlining the practical issues that our clients face across privacy, technology, incident response and litigation. As we look to the year ahead, we remain committed to helping clients navigate the increasingly complex environment with technology decisions that are forward-looking and defensible.
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