J. Mark Stewart was raised in Cheyenne, Wyoming. Mark graduated from the University of Wyoming in 1987 with a Bachelor of Science in Petroleum Engineering. He became a registered professional civil engineer and worked as a highway design engineer and hydraulic engineer. After joining a Wyoming environmental engineering and consulting firm, Mark designed and managed a variety of environmental remediation projects. 

Mark attended the University of Wyoming College of Law and received his Juris Doctor with honor in 2006. During law school, Mark published a case note, An Environmental Federalism Dust-Up:  EPA’s Authority to Override Unreasonable State Permitting Decisions Under the Clean Air Act, 5 Wyo. L. Rev. 99 (2005) and served as a senior staff member for the Wyoming Law Review.

Mark and his wife Janet live in Cheyenne.