On March 22, 2011, he was appointed as chairman of the inaugural Board of Directors of the President's Foundation on Sports, Physical Fitness, and Nutrition.

In 1970, he was the number one high school basketball player in the U.S. coming out of Mansfield, Pennsylvania, and was the biggest recruiting catch early in Coach Lefty Driesell's career at the University of Maryland, beating out rival Coaches Dean Smith of the University of North Carolina and John Wooden of UCLA for McMillen's services.

[7] McMillen signed with the Braves but postponed his entry into the NBA in order to attend the University of Oxford as a Rhodes Scholar.

His home in Crofton was drawn into the Eastern Shore-based 1st District, represented by first-term Republican Congressman Wayne Gilchrest.

[13] In September 2015, McMillen was selected to lead the Division I-A Athletic Directors’ Association as it moved from Dallas to Washington, D.C.[3] He remains President and Chief Executive Officer of the renamed Lead1 Association, now advocating for athletic directors at Football Bowl Subdivision universities.