After his playing career, Millen was president and chief executive officer of the Detroit Lions from 2001 until the 2008 NFL season. His eight-year tenure as head of the franchise led to the worst eight-year record in the history of the modern NFL (31–84, a .270 winning percentage), and resulted in his termination on September 24, 2008. Millen assembled the personnel and coaching staff of the 2008 Lions, which became the first team to go 0–16. This was the worst single-season record in league history until it was tied by the 2017 Cleveland Browns. He is generally regarded among the worst general managers in the history of modern sports.