O'Brien began his career in the Seattle Mariners front office in 1977 (the team'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.
[citation needed] He was assistant general manager of the Texas Rangers from 1997 until changing organizations in 2003.
[2] O'Brien was hired as the general manager of the Cincinnati Reds on October 27, 2003, succeeding Jim Bowden.
[citation needed] O'Brien earned degrees at Rollins College and Ohio University.
[1] His father, Dan O'Brien Sr., was the general manager of three teams in the American League West division from 1974 through 1993: the Texas Rangers, Seattle Mariners (where he also was club president) and the California Angels.