Home » Attorneys » Sumoski, Diane M.

"The art of law is listening to your client, understanding her problem, and employing creativity to solve the problem using the legal palette we have designed through education and experience."

Diane Sumoski’s twenty-six year career at Carrington Coleman has provided her with deep experience in a wide array of sophisticated and important litigation, including the Enron multidistrict litigation, consumer class and other litigation for Kraft Foods, trade secret litigation for Marconi Telecommunications, and family fiduciary litigation that was absolutely critical to her clients. As a result, Diane is listed in the Best Lawyers in America and Texas’ Best Lawyers in both Securities Litigation and Commercial Litigation. She also has been honored for business litigation on the Texas Super Lawyers list published by Texas Monthly magazine.

Diane regularly represents national and multinational corporations and their officers and directors in complex business disputes, including securities litigation, RICO claims, breach of contract, trade secrets, non-compete, and breach of fiduciary duty litigation. Recently, Diane was one of four Carrington Coleman partners responsible for obtaining the complete dismissal on the second day of trial of a bet-the-company, multi-billion dollar, RICO and commercial disparagement lawsuit in New Jersey state court. The wide-ranging allegations and claims in the 150+ page complaint involved some of the largest and most well-known hedge funds on Wall Street. She coordinated the collection and analysis of reams of evidence, including a multi-terabyte document database, in furtherance of an aggressive and thorough strategy that systematically attacked and neutralized the claimants’ charges of a massive conspiracy, ultimately achieving this extraordinary result for the firm’s client.

Diane has also represented individuals in connection with their business and fiduciary duty litigation, as well as their probate and trust and estate disputes. Her experience representing companies and their officers and directors puts her in a unique position to understand the operations of the family and smaller businesses that regularly have an immense impact on the individuals involved in these disputes. In order to counsel and achieve results for these clients, she immerses herself in the business and intangible factors that shape their livelihoods.

Diane has experience in state and federal trial and probate courts throughout Texas. Although she particularly enjoys the challenges and rewards of trying cases before courts and juries, she has handled matters in the Dallas Court of Appeals and Fifth Circuit Court of Appeals as well. She is experienced in a variety of procedural settings, including class action and multi-district litigation, FINRA (formerly NASD) arbitrations, and international arbitrations.

Diane has long been dedicated to serving her community and the bar. She is currently the Director of the W.W. Caruth, Jr. Child Advocacy Clinic at the Southern Methodist University Dedman School of Law, where she teaches child advocacy law and trial skills to her students and represents, as Guardian Ad Litem/Attorney Ad Litem, children who have been removed from their homes by Child Protective Services as a result of abuse and neglect. She is serving in her third term as a member of the Board of Directors of the 11,000+ member Dallas Bar Association, and has been active in the Dallas Volunteer Attorney Program, having been recognized with Legal Aid of Northwest Texas’s Women’s Legal Advocacy Award for her work benefiting women and children.

“I care about helping my clients resolve whatever their problems are. They are my focus, and my efforts are shaped by their specific needs. My goal is to figure out what’s right for them and get it done.”


Probate and Trust & Estate Litigation
Represented client in connection with a family dispute involving a family-held corporation owned by client, her siblings and her remaining living parent through a trust structure created in connection with the parents’ estate plan. Brought action on behalf of client and the family corporation to remedy undue influence of certain siblings in obtaining a larger than intended share of the family estate.

Trade Secrets / Non-Compete / Intellectual Property
Represented a telecommunications company in a series of matters that began when a competitor sought to enjoin four engineers, including a recently hired vice president and plant manager, from joining client firm to develop a new product. Successfully defeated the TRO and Temporary Injunction, resulting in competitor voluntarily dismissing the suit. Continued representing the company in connection with trade secret challenges brought by yet another competitor regarding the new product and in an international arbitration with the Taiwanese subcontractor who developed certain aspects of the product.

Represented accused infringer of patented web site technology. Case was venued in the Eastern District of Texas.

Represented a standardized testing service in bringing claims for trademark infringement and copyright infringement, alleging that a test preparation company obtained unreleased copies of standardized tests to use with its clients.

Represented client in connection with claim against an employee pursuant to the Internet Corporation for Assigned Names and Numbers’ Uniform Domain Name Dispute Resolution Policy and the Computer Piracy Act for misuse of client’s domain name.

Securities Class Actions and Multidistrict Litigation
Represented a Defendant Class in a ground-breaking class action in which a company and its insurers attempted to achieve a global settlement of their past and future asbestos liabilities.

Represented Ken Lay in the Enron securities MDL proceeding.

Represented a major food company in an MDL class action brought by consumers who claimed that genetically engineered corn infiltrated certain food products.

Represented outside directors in a securities class action in the Eastern District of Texas brought as an MDL proceeding in which she acted as court-designated liaison counsel for all Defendants.

Pro Bono
Assisted a grandmother in adopting her grandson to enable him to enroll in school, obtain medical care, and ensure his clear right of inheritance of his grandmother’s worldly goods, including her modest home.

Honors and Distinctions

Named to the Texas Super Lawyers list 2011-2013.

Named for inclusion in the Best Lawyers in America for Commercial Litigation and for Securities Litigation since 2010.

Women’s Legal Advocacy Award from Legal Aid of Northwest Texas (2010).

Named for inclusion in the Dallas edition of Texas’ Best Lawyers.

Dallas Bar Association, Joanna Moreland Outstanding Committee Chair Award (2008 and 2012).

Fellow: American Bar Foundation.

Life Fellow: Dallas Bar Foundation and Texas Bar Foundation.

Listed in Who’s Who in American Law.

Dallas Volunteer Attorney Program Awards for Outstanding Pro Bono Coordinator, 1998, and Pro Bono Coordinator of the Year, 2005.


Moderator, Fiduciary Duty Litigation, C.L.E. presented by the Dallas Bar Association, Judiciary Committee (August 2, 2012).

Author, Determining Jurisdiction for Breach of Fiduciary Duty Claims presented at the Dallas Bar Association Fiduciary Duty Litigation CLE (August 2, 2012).

Faculty, Dallas Bar Association, Trial Academy – Opening Statements Module (2013).

Faculty, Dallas Bar Association, Trial Academy – Evidence Module (2012 and 2014).

Author, A Lawyer’s Professional Responsibility to Provide Pro Bono Legal Services, Dallas Bar Association Pro Bono Activities Committee Pro Bono Summit, 2008.

Author, Expert Advice: Practical Tips for the First Meeting With Your Expert, American Bar Association Annual Meeting, 2008.

Presenter, What Attorneys Want (And Sometimes Even Need) From Their Experts, Forensic Expert Witness Association Continuing Legal Education, May, 2008.

Presenter, Bridging the Gender Gap in the Courtroom, at the Connecticut Defense Lawyers Association’s 2007 “Women in the Courtroom” Continuing Legal Education.

Author, Bridging the Gender Gap, The Litigation Manual, First Supplement 2007.

Author, Enron: Navigating the Civil Side of the Corporate Case of the Century, American Bar Association Section of Litigation Annual Conference, San Antonio, 2007.

Presenter, Creating A Visual Strategy With Your Expert: Using Demonstratives With Expert Witnesses; American Bar Association Annual Meeting, San Francisco, 2007.

Moderator, Examining Expert Witnesses, American Bar Association Section of Litigation Annual Conference, Los Angeles, 2006.

Presenter, Discovery Problems and Their Solutions, American Bar Association Annual Meeting, Chicago, 2005.

Litigation Against Bank Trust Departments; Will Contests and Other Probate Litigation; Fraud and Related Claims; The Hearsay Rule and its Exceptions – Articles included in materials presented at Continuing Legal Education courses.

Court Admissions

Texas, 1987

Texas Supreme Court

U.S. District Courts for the Northern, Southern, Eastern, and Western Districts of Texas

U.S. Court of Appeals for the Fifth Circuit


Cornell Law School
J.D., cum laude, 1987
Associate, Cornell Law Review, 1985-1986; Editor, 1986-1987
Recipient, John J. Kelly, Jr. Memorial Prize, 1987

Franklin and Marshall College
B.A., 1984


Faculty, SMU Dedman School of Law, 2013–present

Board of Directors of the Dallas Bar Association, 2009–present.

Dallas Bar Association, By-Laws Committee, Vice-Chair 2014.

Dallas Bar Association, Judiciary Committee, Co-Chair, 2013.

Dallas Bar Association, Continuing Legal Education Committee, Co-Chair, 2011.

Special Committee on the Future of Multidistrict Litigation of the American Bar Association, Section of Litigation, Co-Chair, 2009–10.

Director of Division VII, ABA Section of Litigation Public Service Division, 2008–09.

Dallas Bar Association / Legal Aid of Northwest Texas, Equal Access to Justice Campaign, Chair of Corporate Division, 2013.

Dallas Bar Association / Legal Aid of Northwest Texas, Equal Access to Justice Campaign, Chair, 2008–09.

Dallas Bar Association / Legal Aid of Northwest Texas, Equal Access to Justice Campaign, Co-Chair, 2007–08.

Dallas Bar Association Community Service Fund, Director, 2008–present.

Dallas Bar Association Minority Participation Committee, Co-Chair, 2009.

Expert Witnesses Committee of the American Bar Association Section of Litigation, Chair, 2004–08.

Dallas Bar Association Pro Bono Activities Committee, 1987–present. Co-Chair, 2008.

Dallas Bar Association, Summer Law Intern Committee, Vice-Chair, 2004–06; Co-Chair, 2007.

Chair of the Host Committee for the 2002 Fifth Circuit Judicial Conference.

Director of Division IV of the American Bar Association Section of Litigation, 2000–01.

Woman Advocate Committee of the American Bar Association Section of Litigation, Chair, 1998-2000.

American Bar Association Section of Litigation programming for the American Bar Association Annual Meeting, Chair, 1995–96.

Member: American Bar Association Section of Litigation and Intellectual Property Law Section, State Bar of Texas, Dallas Bar Association.