[4] He then joined the Islanders' American Hockey League (AHL) affiliate, the Bridgeport Sound Tigers, scoring two goals in his professional debut.

The Otters got off to a slow start, and he was traded to the Saginaw Spirit in late November in exchange for promising centre Zack Torquato.

On February 27, 2007, O'Marra's NHL rights were dealt in a trade to the Edmonton Oilers, along with Robert Nilsson and the Islanders' first-round draft pick in the 2007 (Alex Plante), in exchange for Ryan Smyth.

On March 17, 2011, due to multiple injuries to Oilers players, O'Marra was again recalled to the NHL, along with fellow Oklahoma City Barons – Edmonton's new AHL affiliate – teammates Alexandre Giroux and Chris VandeVelde.

[9] On July 27, 2012, with the impending 2012–13 NHL lockout, O'Marra signed his first European contract on a one-year deal with Lahti Pelicans of the Finnish SM-liiga.

He also played on the Canadian under-18 team that finished with a silver medal at the 2005 IIHF World U18 Championships in Plzeň, Czech Republic.

O'Marra was selected and played a part of the consecutive gold medal-winning Canadian teams at the 2006 and 2007 World Junior Ice Hockey Championships.