In the opening round of the year, against the Wests Tigers, Gallen was involved in a fight which saw him suspended for two weeks after the NRL Judiciary found him guilty of a contrary conduct charge.

Gallen was presented the Cronulla-Sutherland Sharks chairman's Award in 2005 by the club's President Barry Pierce after his impressive season where he led the NRL in both hit ups and off loads.

In June, Cronulla coach Stuart Raper pleaded with the New South Wales selectors to give Gallen an opportunity to prove his worth at State of Origin level.

[15] The Prime Minister's XIII defeated Papua New Guinea 28 points to 8 at Port Moresby but Gallen failed to be selected for the Australian Tri Nations squad.

[18] There were rumours that he would walk out on the club after his contract expired as well as other reports in the media that Manly would sign him as a long-term replacement for a recently retired player, Ben Kennedy.

Gallen stated that he decided to stay at the Sharks because he was inspired by Nathan Hindmarsh, who had recently signed a contract with the Eels in the aim to be a one-club man.

[29] On 11 June, in round 13, Gallen sparked controversy in the local derby match against St. George Illawarra at Oki Jubilee Stadium in which Cronulla triumphed 20 points to 16.

[30] St. George-Illawarra coach Nathan Brown hit out at Paul Gallen claiming that he "is a tough player, that wouldn't have knocked the top off him.

The judiciary charged him with a grade one careless high tackle which in turn meant that he was suspended for the game against South Sydney in the following round.

Before the third game of the Origin series, Gallen declared that he "can't wait to be running out and getting booed, I love that sort of stuff.

[35] But even after Queensland lost their lock in the first minute, both their wingers during the middle of the game and numerous other injuries to players who could not come off due to no more replacements, NSW could not get more than a two-point lead until the 72nd minute where they scored two tries, Gallen setting up the final New South Wales try for Hazem El Masri, which in the process capped off an 18 points to 4 New South Wales victory.

[36] Round 22, against third-placed Parramatta Eels, saw the Cronulla club snap a seven-match losing streak in golden point extra time.

[37] At the conclusion of the NRL Premiership, Gallen was rewarded for his fine season with a call-up for the Australian squad in a one-off test match against New Zealand on 14 October.

However, it was announced barely a week before the match that Gallen had to be pulled out of the squad due to a "shoulder injury", with his replacement being Melbourne Storm's Dallas Johnson.

In the third and decisive game of the series Gallen gave away three penalties and came under heavy criticism from fans for his lack of discipline, in particular for his late hit on Johnathan Thurston.

[45][46][47] Although the Cronulla-Sutherland Sharks sat on the bottom of the 2009 NRL ladder after six rounds, Gallen was named in the preliminary 40-man squad for NSW for 2009's State of Origin series.

[49] The incident gained attention initially, due to the angry reaction of Paea, who is normally a quiet reserved player with strong religious beliefs.

However, his performance was still impressive enough to lead Daily Telegraph Sports editor-at-large, New South Welshman Phil Rothfield, to postulate, that of all the NSW players, Gallen "possibly" would be the only one that Queensland would select if he was theoretically available for them (in place of Ashley Harrison).

Subsequently, there were claims that his performance was fuelled by performance-enhancing substances, with journalist Andrew Webster linking these in an article; "State of Origin 2016: The tough question NSW Blues captain Paul Gallen does not want to answer".

[65] Gallen himself played a key role, setting up Ben Barba for the first try of the night to put his side ahead 8–0.

[69] In November, Gallen spoke to the media in the aftermath of Valentine Holmes leaving the NRL in hopes of gaining an NFL contract.

[74] In Round 9 against the Gold Coast Titans, Gallen scored his first try of the season and also kicked the first goal in his career on the full time siren as Cronulla won 26–18 at Suncorp Stadium.

The panel who voted were made up of Premiership-winning coaches Phil Gould, Craig Bellamy, Trent Robinson and Ricky Stuart along with Hall of Famers Peter Sterling, Darren Lockyer, Danny Buderus and Laurie Daley.

Gallen declined the contract offer, explaining that it would have a massive impact on him and his family and that he would want to stay loyal to Cronulla for the rest of his career.

[83] In 2014, Gallen turned professional after it was confirmed he would fight Australian-based Herman Ene-Purcell on the undercard of Daniel Geale versus Garth Wood.

[86] Prior to the event, Gallen reported he had been admitted to hospital due to experiencing severe pain after contracting golden staph in his groin and underwent surgery privately in Sydney.

[90] His fourth fight was another points decision victory over fellow-rugby league forward Bodene Thompson in a charity event at SkyCity Auckland.

[91] On 20 December 2018, Gallen agreed to return to the ring to fight former professional rugby league footballer John Hopoate with the match being scheduled for 9 February 2019.

[94] Two more victories over Mark Hunt and Lucas Browne had Gallen challenging Justis Huni for the Australian heavyweight title on 16 June 2021.

Since 2018, he has appeared on 100% Footy alongside James Bracey and Phil Gould - a rugby league show that airs on Monday nights on Channel Nine.