Glen Mullins began practicing law in 1976 after graduating from the University of Oklahoma College of Law. He was a law clerk for United States District Judge Fred Daugherty 1976 to 1979 and has worked in the private practice of law since 1979. He has been admitted to practice law in the state of Oklahoma, all federal courts in Oklahoma, and the United States Court of Appeals for the Tenth Circuit.

Glen maintains the highest rating (AV Preeminent) by the Martindale Hubbell Law Directory and has upheld this distinction since 1986. He has also been selected by Oklahoma attorneys as an Oklahoma Super Lawyer since 2009. Glen has frequently lectured at seminars sponsored by the Oklahoma Bar Association on matters involving Trial Practice, Insurance Law, Bad Faith Litigation and Nursing Home Litigation.

After graduating from the University of Oklahoma in 1970 with a B.A. in Journalism, Glen served in the U.S. Army 1970-1972, which included a tour of duty in Vietnam.

Glen and his wife, Mary, live in Edmond, Oklahoma. Their daughter, Laura, lives in Tahlequah with her husband, Tyson, and daughters, Adele (born in 2010) and Wesley (born in 2014). Their son, Mark, lives in Chicago.