Mat served in the Idaho House of Representatives from 2012 to 2019 including as  the House Minority Leader. He focused his work on conservation and public lands issues, rural infrastructure development (rural teacher recruitment, medical residency programs and broadband development), multimodal transportation issues including safe routes to school, and economic development.

As professional mountain guide, Rep. Erpelding was a tireless advocate for conserving our natural environment and for programs that encourage young Idahoans to get outside. He advocated for an Idaho Youth Conservation Corps and believes that experience in the outdoors is essential to protecting our most valuable resources. Mat is a past president of the Association of Outdoor Recreation and Education, and in 2010 was a recipient of the Idaho Business Review’s 40 most accomplished under 40 award.