With over two decades of experience as a litigator, Stuart concentrates his practice in the area of commercial general liability. He routinely handles high exposure matters in the fields of product liability, premises liability, auto liability, construction litigation, marine liability, dram shop and commercial litigation. This includes cases involving personal injuries and property damage claims.
As the Managing Attorney of the firm's third-largest office, Stuart oversees the daily operations, including the supervision of 75 employees. In addition to his managerial duties, Stuart serves as the Casualty Supervisor, where he ensures that all client matters are handled promptly, professionally, and effectively by the team of attorneys.
In his career, Stuart has represented manufacturers, suppliers and retailers in product liability matters, including electronics, medical equipment, food products, appliances, farm equipment, plumbing equipment, power tools, toys and sports and recreational equipment. He frequently represents property owners, retailers, pharmacies, general contractors, subcontractors and utilities in premises liability litigation. He has tried numerous cases to verdict in counties throughout Western Pennsylvania.
A significant portion of Stuart’s practice has been devoted to construction litigation. These cases are highly complex and require deep industry knowledge and experience. Stuart has handled a wide range of construction injury and defect cases, representing contractors, subcontractors, material suppliers, engineers, architects, and other construction professionals throughout Pennsylvania. His experience includes defending against claims involving construction defects such as water intrusion from faulty roofing or window and door seals, cracked foundations or improper waterproofing, structural and design issues, mold intrusion, drywall defects, and soil subsidence, heaving, or movement.
Stuart attended the University of Pittsburgh graduating with a B.A. in Political Science. He then attended the University of Pittsburgh School of Law where he participated in the Appellate Moot Court Program, Student Bar Association and the Health Law Certificate Program. He obtained his juris doctor from the University of Pittsburgh School of Law.
Stuart currently serves on the Marshall Dennehey Diversity, Equity and Inclusion Committee working to improve the recruitment, retention and advancement of diverse attorneys and professionals. He is the former President of the Pennsylvania Defense Institute, an organization of civil defense attorneys, executives of insurance companies and self-insured corporations. Stuart is also a member of the Allegheny County Bar Association and the Academy of Trial Lawyers of Allegheny County. Among his many honors, he is Rated AV Preeminent by LexisNexis Martindale-Hubbell and is recognized among the Best Lawyers in America for his work in product liability litigation. Stuart is additionally recognized as Pennsylvania Super Lawyer.
Honors & awards
AV Preeminent by Martindale-Hubbell
The Best Lawyers in America, 'Lawyer of the Year,' Pittsburgh, Product Liability Litigation - Defendants
2026
The Best Lawyers in America, Product Liability Litigation - Defendants
2022-2026
Pennsylvania Super Lawyers
2018-2022; 2025
Year joined
1998
Results
Defense Verdict Following Jury Trial in Slip and Fall Case in the Court of Common Pleas of Allegheny County.
Premises & Retail Liability
February 6, 2024
The plaintiff slipped in the lobby of a commercial building and claimed a serious and ongoing injury to her right shoulder. She alleged she fell due to a wet floor caused by the facilities management’s cleaning process and the lack of sufficient visible wet floor caution signs. The plaintiff underwent two surgeries, claimed ongoing pain and suffering, and sought $500,000 prior to trial.
Defense Verdict Secured in Slip-and-Fall Jury Trial
Premises & Retail Liability
February 6, 2024
We obtained a defense verdict following a three-day jury trial in a slip-and-fall injury case in the Court of Common Pleas of Allegheny County. The plaintiff slipped in the allegedly wet lobby of a commercial building and claimed a serious and ongoing injury to her right shoulder. Problematic for our case was the lack of a surveillance video of the incident, photographs of the lobby contemporaneous to the incident, or an incident report.
Marshall Dennehey Successfully Represents Client in Multi-Million Dollar Chemical Spill Case
Property Litigation
October 21, 2021
In a lawsuit seeking $279 million in alleged property damages, Marshall Dennehey attorneys successfully defended their client, a subcontractor of a railroad repair shop, against any and all liability.
Thought Leadership
98 Marshall Dennehey Attorneys Recognized in the 2026 Editions of The Best Lawyers in America and the Best Lawyers: Ones to Watch in America
August 20, 2025
Marshall Dennehey is proud to highlight the firm’s 98 attorneys who have been recognized in the 2026 editions of The Best Lawyers in America and the Best Lawyers: Ones to Watch in America. Less than 6% of all practicing lawyers in the U.S.
Marshall Dennehey Announces 2025 Pennsylvania Super Lawyers and Rising Stars
May 22, 2025
Thirty-three attorneys across Marshall Dennehey's five Pennsylvania offices have been selected to the 2025 edition of Pennsylvania Super Lawyers magazine.
How I Made Office Managing Partner: 'Stay True to Yourself, and Things Will Work Out to Your Benefit,' Says Stuart Sostmann of Marshall Dennehey
Pittsburgh
January 3, 2025
Stuart H. Sostmann Named Managing Attorney of Marshall Dennehey’s Pittsburgh Office
September 3, 2024
Stuart H.
On the Pulse...Construction Injury Litigation Practice Group
Philadelphia - Headquarters
Pittsburgh
Construction Injury Litigation
December 1, 2023
Recent data released from the United States Bureau of Labor Statistics reveals that construction laborers accounted for 11.9% of all reported fatal falls, slips, or trips in 2020 across all occupations. Defense Digest, Vol. 29, No.
Classes/Seminars Taught
AI in the Legal Profession, Marshall Dennehey Client Presentation, September 2024
Civil Litigation State of Affairs - The Impact of COVID-19 in Pennsylvania and New Jersey & What’s Next , Marshall Dennehey Client Webinar, May, 2021
An Overview of Construction Defect Litigation in Pennsylvania, Nationwide Insurance Company, December 16, 2014
Commercial Defense Practice in New York, New Jersey & Pennsylvania, Nationwide Insurance Company, December 5, 2014
Brief Overview of Pennsylvania Contractual Indemnity and Additional Insured Issues, Nationwide Insurance Company, April 2012
Discoverability and Proper Use of Claim Notes, Berkley Mid-Atlantic, October 2011
Media Commentary
'How I Made Office Managing Partner: 'Stay True to Yourself, and Things Will Work Out to Your Benefit,' Says Stuart Sostmann of Marshall Dennehey,' Law.com, January 3, 2025
