O'Brien was drafted by the New England Revolution in the third round of the 1999 MLS College Draft. He never played for the Revs before being waived on March 31, 1999. On April 5, 1999, the San Jose Clash claimed O'Brien in the waiver draft. He spent most of the season on loan with MLS Pro-40 and only four games with the Clash first team before being released at the end of the season. In 2000, he signed with the San Diego Flash of the USL A-League. At some point, he also played for the Sacramento Knights of the World Indoor Soccer League.