Career
Undrafted, O'Neill played collegiate hockey with Yale University of the ECAC before signing a one-year entry-level contract with the Los Angeles Kings at the conclusion of his senior year on March 15, 2012. In the 2014–15 season, his third full season within the Kings organization, O'Neill was assigned to continue to play with the Manchester Monarchs of the AHL. Prior to the 2015–16 season, O'Neill attended the Kings training camp and participated in the pre-season. O'Neill was unable to earn a roster spot in Los Angeles and as a result on the eve of the season, on October 6, 2015, the Kings traded O'Neill to the New Jersey Devils in return for a conditional 7th round pick.
O'Neill made his NHL debut with the Devils on October 10, 2015 against the Washington Capitals.
