He quickly became an NRL premiership regular for the St George Illawarra Dragons and was in the running for the 2003 Dally MRookie of the Year award before the awards were cancelled due to industrial action from the Rugby League Players' Association. Firman continued with the Dragons in 2004, but broke his leg playing Premier League in round 3 after being dropped in favour of Mathew Head. Head impressed many observers, and it became obvious at the end of the season that the Dragons would have to choose between the two players as they could not afford both under the NRL salary cap. The Dragons chose to re-sign Head, despite Firman still having a year on his contract with the club.
2005
Firman moved to the Sydney Roosters for 2005, with coach Ricky Stuart hoping for him to form a combination with Brett Finch in order to replace retiring great Brad Fittler. The Roosters had a bad start to the year, and Firman was soon dropped to Premier League and was seemingly unwanted by the club. He was released mid-season to join with the Cowboys, where he partnered 2005 Dally M medal winner Johnathan Thurston in the halves. The Cowboys reached the finals for the second successive year after finishing in 5th position, and despite being beaten 50-6 by the Wests Tigers in the first week, they beat Melbourne Storm in the second week, and then the Parramatta Eels in the preliminary final, with Firman scoring an important try, putting the club in their first ever Grand Final, against the Tigers. Firman played from the interchange bench in the 2005 NRL Grand Final loss.
2006-2007
Firman trialled with the Penrith Panthers over the 2006 offseason after gaining an early release from the North Queensland Cowboys, he was finally awarded a full-time contract to play with the Penrith club for the 2007 NRL season after their second trial match against the Gold Coast Titans on 3 March. Firman played two games for Penrith in the 2007 NRL season. His final game for the club was in round 17 against the Wests Tigers where Penrith were defeated 43-26 at Telstra Stadium. Penrith would finish the season in last place on the table. He was later released by the Penrith club.
2002 NZ tour sexual assault investigation
While on a tour of New Zealand in February 2002, members of the Cronulla Sharks were involved in a group sex session of disputed consent with a young woman in a Christchurch hotel room. The New Zealand police "... noted that some comments she made suggesting she was not distressed were a mechanism for coping with what had happened." Detective Superintendent Neville Jenkins described Clare as naive, young for her age and "...just a growing up teenager." The ABC TVFour Corners program "Code of Silence", broadcast on 11 May 2009, reported the incident, where both Matthew Johns and Brett Firman spoke with Four Corners off-camera, and stated that they were the first players to have sex with Clare; Firman saying that "she was up for it a hundred per cent". Johns has been withdrawn from his various public facing roles despite his public apology. No other players involved, including Brett who was named, have done so to date.
