Cullen is an attorney with Sommer, Udall, Sutin, Hardwick & Hyatt, P.C. in Santa Fe.. He is an experienced cyclist, backpacker, river runner, cross-country skier, and gardener. He has been a member of the Quivira Coalition for more than ten years, and manages its Red Canyon Reserve in Socorro County, New Mexico.
Cullen was born in Dallas, Texas, and grew up in El Paso. He earned a B.A. from St. John’s College in 1980. When he was not in school, Cullen worked in residential housing construction, as a ski instructor, as a native plant landscaper, and as a deck hand on a halibut boat in Homer, Alaska. He resumed his studies at the University of Texas School of Law, and earned a J.D. from that institution in 1984. He is a member of the state bars of New Mexico and Texas, and also practices in federal court.