Simpson returned to University of Wyoming and in 1962 earned his Master of Arts degree, with his thesis, "A History of the First Wyoming Legislature". He would be a member of that body some two decades thereafter. Simpson thereafter earned his Ph.D. from the University of Oregon in Eugene, Oregon. His dissertation on the cattle industry was later published as a book, "The Community of Cattlemen: A Social History of the Cattle Industry in Southeastern Oregon, 1869-1912," (Moscow: University of Idaho Press, 1987). He is a member of the fraternity Alpha Tau Omega. In the early 1970s, Simpson returned to Wyoming to accept a position as the assistant to the president at Casper College in Casper, the state's second largest city. He then became dean of instruction at Sheridan College. After his legislative service ended in 1984, Simpson left Sheridan to become vice president for development at the University of Wyoming and the executive director of the UW Foundation. He resigned from UW to run for governor but returned in 1987 as vice president for development and alumni affairs. Thereafter, he was elevated to his terminal position of UW vice president for institutional advancement. After retirement in 1997, Simpson remained in Laramie and taught history on an adjunct basis at UW and was in 1999 and 2000 the Milward Simpson Distinguished Visiting Professor, named for his father. The Simpson Fund has financed various speakers of different backgrounds and disciplines to UW, including former United States Secretary of State James A. Baker, III, former United States Secretary of the Interior James G. Watt, U.S. President Gerald R. Ford, Jr., and ABC journalist Sam Donaldson. Over the years, Simpson has emceed various UW events. In 2009, he was inducted for "Special Achievement" into the UW Athletics Hall of Fame. While at UW, Simpson and his brother, Alan, were invited to team teach for one semester only by the political science department, but Pete Simpson was still teaching the course twelve years later. After he left the U.S. Senate, Alan Simpson became a lecturer for several years for the Institute of Politics at the Kennedy School of Government at Harvard University, but he returned to Cody in 2000 to practice law with his two sons, Colin and William Simpson. Long involved in civic affairs, Pete Simpson in 2010 joined his former gubernatorial rival, Mike Sullivan, at a fundraising appearance in Rock Springs in southwestern Wyoming for the benefit of the library in Sweetwater County. Pete Simpson narrated the hour-long documentary "Over Wyoming" which was produced by WyomingPBS in 2016.