O'Brien was fired from this position by new Reds ownership on January 23, 2006. He then served as a special assistant to Milwaukee Brewers GM Doug Melvin from 2007-2009.
O'Brien began his career in the Seattle Mariners front office in 1977 (the M's inaugural season), then switched to the Houston Astros in 1982, serving first as the team's farm system director and then its scouting director through 1996. He was assistant general manager of the Texas Rangers from 1997 until his appointment to the Cincinnati post in 2003.