After setting the scoring record at the US National Development Program, Patrick O'Sullivan was selected 1st overall in the 2001 OHL draft. The following season he was the OHL and CHL rookie of the year in 2002. He remains the all-time leader in games, goals, assists and points for the Mississauga/Niagara franchise in the OHL. His junior career was capped off by winning a gold medal with Team USA at the 2004 World Junior Championship.

O'Sullivan was a 2nd round pick in the 2003 NHL Entry Draft. After his first pro season, he was Rookie of the Year in the AHL after scoring 52 goals and 103 points. He then played eight seasons in the NHL with the Los Angeles Kings, Edmonton Oilers, Minnesota Wild and Arizona Coyotes. He finished his pro career playing for IFK Helsinki in the Finish Elite League.

O'Sullivan represented the United States internationally eight times including three World Championships.

After retiring as a player, O’Sullivan worked in the media for TSN covering the NHL on radio and television as well as consulting on player development for pro and junior teams.