Thomas M. Sims is an attorney in the Opioid Litigation Group at Baron & Budd. Since joining the firm in 1999, he has spent most of his career litigating complex environmental cases ranging from pharmaceutical injuries to water contamination to air pollution.

He was lead counsel in one of the largest Proposition 65 cases in history. Proposition 65 is a California state law that permits private citizens to enforce certain environmental regulations on behalf of the public. Mr. Sims represented three environmental groups in their efforts to reduce diesel exhaust emissions from school buses. Working as lead counsel, he was a driving force in securing a settlement in which the defendant agreed to invest more than $28 million to replace or retrofit school buses that were built before 2003 with air pollution control devices.

Mr. Sims has worked on behalf of communities that were harmed by toxic releases from nearby industrial activities. In 2006 he received the Trial Lawyer of the Year award from the non-profit Public Justice in connection with his work on a long-running insurance coverage dispute. Originally filed in 1985, the case involved groundwater contamination of public aquifers in Tucson, Arizona. As a result of the efforts of Mr. Sims and his co-counsel, the case finally settled in 2005. During the intervening twenty years, Baron & Budd won two trials and prevailed on three separate appeals. Mr. Sims also represented the Governor of the State of Louisiana in his efforts to secure natural resource damages resulting from the BP Oil Spill.

Mr. Sims has also represented whistleblowers under state and federal false claims acts. He represented two mechanics who alleged that their former employer, the largest school bus operator in the country, consistently shortcut health and safety procedures in order to increase profits. In connection with his work on that case, Mr. Sims persuaded the California Court of Appeals to adopt the theory of implied certification as a basis for liability under the California False Claims, the first time a California court adopted this theory.

Mr. Sims currently devotes the majority of his time to seeking compensation on behalf of individuals and public entities that have been harmed by unsafe prescription drugs. Mr. Sims is proud to be part of Baron & Budd’s Opioid Litigation Group, which assists communities that have been devastated by the opioid epidemic. Previously, he was part of the litigation team that helped seven states’ attorneys general recover a $177 million settlement against GSK regarding its fraudulent marketing of the diabetes drug Avandia.

Reported Cases

  • San Francisco Unified School District, ex rel. Contreras v. Laidlaw Transit, Inc., 213 Cal. App. 4th 1212 (Cal.App. 2013)
  • San Francisco Unified School District, ex rel. Contreras v. Laidlaw Transit, Inc., 224 Cal. App. 4th 627 (Cal.App. 2013)
  • San Francisco Unified School District, ex rel. Contreras v. Laidlaw Transit, Inc., 182 Cal. App. 4th 438 (Cal.App. 2010)
  • In re Katrina Canal Breaches Consolidated Litigation, 647 F.Supp.2d 644 (W.D. La. 2009)
  • Fullen v. Philips Elec. N. Am. Corp., 266 F.Supp.2d 471 (N.D.W. Va. 2002)
  • Hamilton v. Beretta U.S.A. Corp., 96 N.Y.2d 222, 750 N.E.2d 1055, 727 N.Y.S.2d 7 (2001)

Significant Trials

  • Environmental Law Foundation v. Beech-Nut Nutrition Corp., et al., No. RG-11597384 (Super. Ct., Alameda County, Cal.)
  • In re Katrina Canal Breaches Consolidated Litigation, No. 05-4182 (E.D. La.)
  • Smith, et al., v. Tucson Airport Authority, No. C-251422 (Super. Ct., Pima County, Ariz.)


University of Texas School of Law (J.D., with honors, 1999)

New College (B.A. 1996)

Bar & Court Admissions



United States District Court for the Northern, Eastern, Southern and Western Districts of Texas

United States District Court for the Northern and Southern Districts of California


Trial Lawyer of the Year (Public Justice, 2006)

Rising Star of Texas Law (Thompson Reuters, 2005, 2011)

Top 100 Civil Plaintiff Trial Lawyers (National Trial Lawyers, 2017)

Professional Associations

American Association for Justice

Texas Trial Lawyers Association

Public Justice Association