He started the 2003 NRL season at South Sydney after leaving Brisbane. He only played 5 games for the club. Walker requested a release from his contract sighting personal reasons. At the time Walker was on $350,000 a season with Souths. In 2015, Walker spoke to the media about his time at The Rabbitohs and said he was sent death threats after walking out on the team by fans. Walker said "Yes I had about 7-8 letters, I still don't why or who sent them, the worst one was when I received a letter from someone saying they were going to shoot me, I went to the game thinking I was going to die".
Sydney Roosters
After leaving Souths mid-season, Walker joined the club's arch rivals the Sydney Roosters. Walker was a try-scorer in the Sydney Roosters' loss in the 2003 NRL Grand Final against Penrith. He gained a reputation as a "bad boy" of rugby league. In the 2004 NRL season he was involved in a drunken altercation with police outside a Fortitude Valley nightclub The Roosters club fined the winger and placed him on an alcohol ban for the rest of the season. He returned to play on the wing and score a try for the Roosters in their 2004 NRL Grand Final loss to cross-Sydney rivals, Canterbury-Bankstown.
Melbourne Storm
After departing the Sydney Roosters following the conclusion of the 2005 NRL season, Walker signed for Melbourne. In August, 2006, Walker was sacked by Melbourne Storm for disciplinary reasons. In 2019, Walker spoke about his dismissal from Melbourne and also his departure from the Sydney Roosters saying "I had a bit of a disagreement with 'Sticky' at the end of 2005. I’d been getting on the drink pretty heavy and my relationship was falling to bits. I signed with Melbourne, and it was the same thing down there. I didn’t curb my ways off the field, and that didn’t fit in with their culture. The disagreement between Craig Bellamy and myself was brought on by me being irresponsible off the field".
In November 2006, it was announced that he had been given a trial with the Gold Coast Titans. In early March 2007 after a series of strong performances in pre-season trial matches with the Titans, Walker signed a one-year deal with the Gold Coast club. In the first NRL premiership game for the new club Walker scored two tries, but then broke a bone in his hand early in the second half. In April, 2007, while sidelined with injury, Walker was reported to have been ejected from a bar after for "bad behaviour". The Gold Coast Titans suspended him as a result and it was later revealed that Walker had been suffering from alcoholism and an anxiety disorder. After a period of rehabilitation and several games in the Queensland Cup, Walker returned to the NRL in Round 19 against Canterbury. In 2008, Walker suffered a season-ending ruptured Achilles tendon for the second time in five months. In 2009 he attracted interest from Super League clubs, but said he did not want to play in Europe and he would prefer to stay in the NRL with a Queensland team.
Catalans Dragons
After departing the Gold Coast, Walker signed a two-year deal with the Catalans Dragons in France.
Walker returned to the NRL in 2011 to play with the Parramatta Eels. He approached Parramatta officials for permission leave the NRL club after a string of injuries. Walker retired from the NRL at the end of the 2011 season.
