while he was never drafted in the nhl, o'brien was invited to the san jose sharks training camp in 2010. he then returned to the acadie-bathurst titan for the 2010–11 season where he led all first year players in goals and points and set a new team record for goals scored. he also tied réal godin as the only player in qmjhl history to record no penalty minutes while accumulating at least 50 points in a season. as a result of his play, o'brien was named to the 2011 subway super series roster to play in an exhibition tournament against the russian national junior team. he ended the season with a career-high 101 points and won the frank j. selke memorial trophy as the qmjhl most sportsmanlike player. he was also named a finalist for the rds cup as rookie of the year and michel bergeron trophy as offensive rookie of the year.