[1] He was also chosen to play for Bobby Orr in the Canadian Hockey League (CHL) Top Prospects Game.

In his first career playoff series against the Detroit Red Wings in 2004, he tied the team high with three points (one goal and two assists).

During the 2004–05 NHL lock-out, Hartnell helped Vålerenga win the Norwegian Championship, scoring 12 goals in 11 playoff games.

The following season, Hartnell continued to produce similar offensive numbers, also setting franchise records for career penalty minutes (461)[4] and for the fastest two goals by an individual (23 seconds).

[6] On June 18, 2007, Hartnell, along with Kimmo Timonen, were traded to the Philadelphia Flyers in exchange for a first-round pick previously acquired from Nashville for Peter Forsberg.

While he registered his first point as a Flyer in the home opener,[10] his first goal (an empty netter) did not come until the 16th game of the season.

Playing mostly on the left wing of centre Jeff Carter, he posted a career-high in all offensive categories, scoring 30 goals and 30 assists for 60 points in 82 games.

Hartnell himself struggled at the beginning of the following season, with only two points in his first seven games, but would heat up after being placed on a line with Jaromír Jágr and Claude Giroux.

In a late regular season game against Pittsburgh, Hartnell mocked a Penguins fan dressed as Hulk Hogan sitting directly behind the Flyers bench.

This caused the Flyers organization to create a special T-shirt with Hartnell's "Hogan" gesture on it, which was given to every fan in attendance for Game 3 of the Eastern Conference Quarterfinals against the same Penguins.

In addition to his poor scoring, his play caused him to be taken off of his normal line at times, which was centred by Flyers captain Claude Giroux.

[20] On July 1, 2017, Hartnell returned to the Predators, signing a one-year, $1 million contract, reuniting him with former Flyers coach Peter Laviolette.

[26] A previous Penguins-related incident showcased Hartnell's good nature in an interaction with a Penguins fan taunting him with an orange wig and Flyers number 19 jersey bearing the name "Fartsmell" in a game played in Pittsburgh on March 22, 2009.

[27][28][29] Similar to a Gordie Howe hat trick, a Harttrick occurs when a player has a goal, a fight and a fall in a game.

During the 2012 Stanley Cup Playoffs, Hartnell was seen mocking a Penguins fan dressed as Hulk Hogan behind the Flyers bench, which drew laughter from the television broadcast team working the game.

[31] Hartnell is, together with his former Flyers teammates Kimmo Timonen and Sami Kapanen, one of the owners of the Finnish Liiga hockey team KalPa.