His first season at the new joint-venture of the St. George Illawarra Dragons was marred by controversy as the incessant media hype over an alleged feud with Anthony Mundine and whether by playing out of position at half-back was affecting his form.

With the shock departure of Mundine from St. George Illawarra in 2000, Barrett was allowed to move back to his original position of five-eighth and he received the Dally M Medal in 2000.

[citation needed] Barrett had two years left on his St. George Illawarra Dragons contract, but a get-out clause enabled him to quit the club for a move to England.

[citation needed] Barrett made his Wigan Warriors début in a 16–10 defeat against Warrington at the JJB Stadium on 9 February 2007.

Following a release from the final year of his three-year contract with Wigan, Barrett signed with the Cronulla-Sutherland Sharks in June 2008, on a two-year deal, commencing in 2009.

In his Origin comeback, Barrett was charged following a reckless tackle on Queensland's Greg Inglis, and as a result was suspended for two club matches.

The club was also plagued with infighting and there were reported disagreements between Barrett and the Manly owners over lack of chairs and whose responsibility it was to provide them.

[14] On 6 August 2019, Barrett spoke to the media and said that in some way he deserved credit for Manly's form reversal in 2019 which saw the club go from finishing second last in 2018 to contenders the following season.

Barrett said "I’d actually like to think I left them well-educated, A few of the boys I got there like Siro (Curtis Sironen) were coming out of reserve grade, No one else wanted Moses Suli.

I sit back and watch and read people take credit for many things and it’s hard to digest at times because I know who has been and continues to be instrumental in driving a lot of the change behind the scenes but I won’t accept this at all.

[19] In round 7 of the 2021 NRL season, Barrett earned his first win as Canterbury-Bankstown head coach after the club snapped a six-game losing streak to beat Cronulla-Sutherland 18–12.

[21] At the end of the 2021 NRL season, Canterbury finished last on the table and claimed their sixth Wooden Spoon after winning only three matches all year.

[27] In Barrett's first game as interim head coach, Parramatta would lose 42-26 against the bottom placed South Sydney team who were missing eight players and only had one previous win to their name before the match.