For five years following law school, Leopold practiced law in the Rio Grande Valley of Texas in the area of real estate transactions. He joined the St. Mary's faculty in 1967 and earned his Bachelor of Arts degree in history in 1970.
Leopold received St. Mary’s University’s first Distinguished Faculty Award for the School of Law in 1984. As the author of legal treatises, he was the most prolific scholar of his generation on the law faculty.
Leopold’s contributions to the development and clarification of Texas law have been cited by courts and have benefited people in every part of this state.