Gov. Brian Sandoval, himself a former federal judge, said Pro's "knowledge and judicial temperament will be an asset to the commission."
Pro, 68, was appointed to the federal bench by President Ronald Reagan in 1987. He retired in 2012 and took senior status. Pro joined JAMS, an alternative dispute and resolution services center, earlier this year and currently provides arbitration and mediation services.
Pro retired from the U.S. District Court in January and no longer sits as a senior judge.
"I am honored to accept the appointment," Pro said in a statement.
Mulroy resigned to accept a position as a member of the Wynn Resorts Ltd. board of directors. The appointment was approved by the Nevada Commission on Ethics by a 4-2 vote, allowing Mulroy to avoid the state's one-year cooling off period for gaming regulators.
"Judge Pro is a well-respected member of our community with a legal career that has spanned decades of growth in Nevada," Sandoval said. "I know he will serve with integrity and we are fortunate that he has accepted this new position."
During his tenure on the federal bench, Pro served as chief judge for the District of Nevada from 2002 to 2007. Pro was a U.S. Magistrate Judge from 1980 to 1987.
Pro served as co-chair of the advisory board for the founding of the William S. Boyd School of Law at the University of Nevada at Las Vegas, and serves currently on the Boyd School of Law Advisory Board. He serves also as a member of the board of the Saltman Center for Conflict Resolution at the Boyd School of Law.