[1] After graduating college, Mannion began his sports management career in Major League Baseball, spending 16 years with the Philadelphia Phillies from 1982 to 1997.
[2] Mannion left the Phillies in 1997 for a position as Senior Vice President of Ascent Sports in Denver, Colorado.
[1] He later worked in the NFL for the Baltimore Ravens, serving eight seasons as Senior Vice President of Business Ventures from 1999 until 2007.
He served as Executive Vice-President and Chief Operating Officer from November 2007 until March 2009 when he was promoted to President and CEO.
During his tenure, the Dodgers led the league in game attendance, set a World Record for the largest attended baseball game in 2008 at the LA Coliseum (119,000), hosted the 2009 World Baseball Classic championship rounds, and reached the National League Championship Series two consecutive years.