Mary T. SullivanMary T. Sullivan

Licensed Texas Attorney

Nacol Law Firm P.C.

Walnut Hill Tower
8144 Walnut Hill Lane, Suite 1190
Dallas, Texas 75231
Metro: (972) 690-3333


Mary Therese Sullivan was admitted to practice in New York State in 1985, after graduating summa cum laude with a B.S. in Education from the State University of New York College at Buffalo and earning a J.D. from the State University of New York at Buffalo School of Law. Mary began her legal career at Gannon, Gannon & Sullivan in Buffalo, where she practiced primarily in the areas of family law and criminal defense. She litigated divorce actions and frequently was court-appointed to serve as law guardian for vulnerable children in cases involving abuse/neglect, juvenile delinquency, and custody/visitation matters. She also provided public defense services through the Erie County Bar Association Aid to Indigent Prisoners Society and was a member of its Professional Standards Committee. She tried dozens of felony cases to verdict, including several homicides.

Mary headed west with her family in 2000, settled in Addison, and was admitted to the State Bar of Texas later that year. Until recently, she worked primarily in healthcare law. She has assisted in the defense of physicians in medical malpractice actions, disciplinary matters before the Texas Medical Board, peer review proceedings, and false claims investigations; counseled clients about Anti-Kickback/Stark, HIPAA, and other federal laws; helped providers with billing disputes involving Medicare, Medicaid, and private insurers; addressed credentialing problems; reviewed and revised employment contracts; and drafted policies and procedures for employees and patients to better enable doctors to manage their practices. She has also offered guidance to small businesses regarding entity formation; employee hiring, promotion, and termination; non-compete and non-disclosure agreements; and requests for ADA accommodation and FMLA leave.

Mary and her husband of 25 years still live in Addison with their geriatric dogs and cat. In addition to being active in animal rescue, Mary volunteered as an on-air reader of newspapers and periodicals for the visually impaired with the Niagara Frontier Radio Reading Service and with North Texas Reading & Radio Resource and has counseled clients through the Dallas Volunteer Attorney Program, which named her the Outstanding Volunteer in the East and West Legal Clinics in 2003 and 2004.

Bar & Court Admissions

  • New York State Bar Association, 1985
  • State Bar of Texas, 2000
  • U.S. District Court for the Northern District of Texas, 2003
  • U.S. District Court for the Eastern District of Texas, 2006


  • B.S. in Education, State University of New York College at Buffalo, 1981
    Honors: Summa Cum Laude
  • J.D., State University of New York at Buffalo School of Law, 1984

Mary Sullivan’s Areas of Practice:
Civil Law

  • Consumer Fraud & Deceptive Trade Practices
  • Contract Disputes
  • Insurance Coverage
  • Professional Liability

Business, Commercial, & Corporate Law

  • Contract Negotiations
  • Employment Matters – ADA Accommodations, FMLA Leave, Violation of Non-Disclosure Agreements, Wrongful Termination
  • Medical Practice Matters – Credentialing, Patient Privacy, Practice Management
  • Non-Profit Formation & Operation

Family Law

  • Child Custody, Support, & Visitation
  • Divorce
  • Pre- and Post-Nuptial Agreements
  • Spousal Maintenance

Real Estate Property Law

  • HOA Law – Rights & Responsibilities of Property Owners
  • Lease Negotiations
  • Home Construction Contracts
  • Lien Disputes
  • Mineral Rights
  • Neighbor Conflicts
  • Purchase & Sale of Commercial & Residential Real Estate

Arbitration and Mediation


8144 Walnut Hill Lane
Suite 1190
Dallas, Texas 75231
Office Hours
Monday – Thursday, 8am – 5pm
Friday, 8:30am – 5pm




Attorney Mark A. Nacol is board certified in Civil Trial Law by the Texas Board of Legal Specialization