Mark D. Sullivan

Mark D. Sullivan is the Principal of his own Jackson Hole law practice, serving individuals and businesses in Wyoming. His work includes environmental law, civil litigation, land use and real estate, construction disputes, and business matters. His clients include ranchers, developers, contractors, environmental organizations, homeowners associations, and small businesses. He represents parties seeking to advance projects as well as clients opposing activities that affect their property or interests.

Sullivan earned a J.D. and an LL.M. from Pace University and a B.A. from Kenyon College. His advanced legal study focused on environmental law, complementing his work in regulatory matters and litigation. He began his legal career with Riverkeeper, Inc., an environmental organization based on the Hudson River, and pursued graduate study while working. That experience connected formal legal training with public interest advocacy and the practical implementation of environmental protections.

Sullivan later worked in the environmental practice group at Carter Ledyard & Milburn, handling impact review, permitting, and related litigation. He relocated to Wyoming in 2003 and established his own firm in 2006. His experience includes state and federal trials, appellate advocacy, and construction arbitration. He has represented clients in property purchases and sales, homeowners association disputes, construction contracts, and environmental challenges involving neighboring uses and federal agency activities.

Mark D. Sullivan emphasizes responsive, personalized attention and an understanding of each client’s objectives. His practice also includes workers’ compensation claims and personal injury matters, along with business formation and governance. He has advised enterprises in technology, alternative energy, hospitality, and construction. By combining transaction advice with experience in contested proceedings, he helps clients evaluate agreements, address regulatory obligations, and determine when negotiation or litigation offers a practical path forward.

Law Office Affiliations

• Principal, Mark D. Sullivan, P.C.
• Member, Wyoming State Bar
• Counsel, Teton Board of REALTORS

Licensed State

• Wyoming

Awards & Badges