O'Reilly would return for the 2005–06 OHL regular season as a third year Spitfire veteran to truly lead by example, setting the team scoring pace by tallying 18 goals and 81 assists (tied for 3rd in the league with Wojtek Wolski).

[4] After a successful debut season with Metallurg, due to injury O'Reilly failed to replicate his form and was released from his second year after only 14 games.

On November 19, 2013, O'Reilly signed a standard player contract (SPC) for the remainder of the 2013-14 season with the Utica Comets of the AHL.

On July 2, 2014, O'Reilly signed a contract with the Comets parent NHL club, the Vancouver Canucks on a one-year deal.

On July 1, 2015, O'Reilly signed a two-year one-way contract with the Buffalo Sabres, worth $700,000 per year, uniting him with his newly acquired brother Ryan.

[6] Entering the 2016–17 season, O'Reilly continued his second year within the Sabres organization as the captain of AHL affiliate, the Rochester Americans.

[7] On July 1, 2017, O'Reilly left the Sabres as a free agent, signing a two-year, two-way deal with the Minnesota Wild.

[12] His younger brother Ryan has played with the Colorado Avalanche, Buffalo Sabres, St. Louis Blues, Toronto Maple Leafs, and Nashville Predators.