Gregory graduated from the University of Nevada, Las Vegas with a degree in business management. After graduation, Gregory went to work for his family business, Pahrump Utility Company Inc., and climbed his way to general manager.

Gregory is the Chairman of the Desert View Hospital Board and a member of the Nevada Taxpayer Association. He previously chaired the Pahrump Regional Planning Commission, Pahrump Capital Improvement Advisory Committee, chaired the Pahrump Ground Water Management Plan Advisory Committee and has participated in developing numerous Nye County Ordinances and Nye County comprehensive plans.

In December of 2018, Gregory was appointed to fill the vacant Assembly District 36. During the 80th Session of the Nevada Legislation, Assemblyman Gregory Hafen II served on the Assembly Committees on Government Affairs, Health and Human Services, and Taxation.