Fletcher's junior club was the Paddington Colts in the Eastern Suburbs District Junior Rugby League. He started his top-level career at the Sydney Roosters in the second row in the 1997 ARL season. Despite only 24 National Rugby League appearances, Fletcher was selected for the Australian team to compete in the end of season 1999 Rugby League Tri-Nations tournament. In the final against New Zealand he played at second-row forward in the Kangaroos' 22-20 victory. Over the years Fletcher would gain 13 caps for the Australian national side and also play 14 games for New South Wales in the State of Origin matches.
One of the highlights of Fletcher's Sydney Roosters career was his appearance at second-row forward in the 2000 NRL Grand Final, their first in 20 years. He also helped Australia inflict a humiliating defeat on the New Zealand national team 52–0 as well as a 3–0 whitewash of Queensland in the State of Origin series.
Fletcher achieved even more success in the 2002 season. He played for the Roosters from the interchange bench in their 30-8 win over the New Zealand Warriors in the 2002 NRL Grand Final in front of 80,130 fans at the Telstra Stadium. It was Fletcher's final appearance for the club (making a total of 125 appearances for the red, white and blue) before moving to rivals the South Sydney Rabbitohs.
Fletcher left the Roosters and moved to perennial strugglers the South Sydney Rabbitohs in 2003. Fletcher was soon installed as the club's captain after signing due to his playing pedigree. In 2003 he won the George Piggins Medal as the club's best and fairest player of the season.
The Rabbitohs' captaincy was stripped from him after an altercation on the pitch with Parramatta Eels player Dean Widders in which Fletcher made a racially based comment towards Widders. It turned out to be the turning point in the Rabbitohs' season, with Ashley Harrison taking the captaincy from him and the Rabbitohs winning most of their matches under him in a late season surge which saw them avoid a third consecutive wooden spoon.
He later apologised for the event, saying: "I apologise unreservedly for comments that I made to Dean Widders in yesterday's game. The comments were totally unacceptable and for that I am sorry. "My actions have set a very poor example for kids who follow Rugby League and these types of comments cannot be tolerated in our game."
Before the scandal that led to Fletcher being stripped of his captaincy, banned for 1 game and fined A$10,000 he had agreed to a move to England to play for Super League outfit Wigan Warriors after two years at Souths. Fletcher joined the Wigan club in 2006 in time for the pre season training but was sidelined for the opening four rounds of Super League after needing emergency Bowel Surgery in early January.
Fletcher's début came against Warrington Wolves on 10 March 2006 at the JJB Stadium in Wigan, and made an instant impact as a substitute scoring his first try three minutes into his first appearance. He was one of the stalwarts that helped Wigan through one of the most tumultuous times in the club's history on and off the field in 2006 with the dismissal of coach Ian Millward, the low morale within the team and seeing the once feared Wigan club sitting at the bottom of the table. Thanks to Fletcher's impact in the Second-row and the Prop positions Wigan managed the seemingly impossible and survived relegation from the Super League, finishing 7th and just missing a playoff place to local rivals Warrington.
Fletcher has begun pre season training with Wigan for the 2007 season, and played in the club's first friendly over the weekend against Huddersfield Giants in which Wigan lost 24–22.
At the end of the 2007 Super League season, Bryan Fletcher retired from competitive rugby league. He had played in 125 games for the Sydney Roosters, 45 for Souths, and a further 55 for Wigan. He also played 2 games for City Origin, 14 State of Origin games for NSW and 13 Test and World Cup matches for Australia.
When he retired from playing in 2007, Fletcher and his business partner Craig Markham began a cleaning company called Cleanfit. The company cleans a number of pubs, clubs and office blocks in Sydney. It also allows Fletcher, who is a qualified plumber, to utilise his trade in order to help with the business.
In 2013, Bryan Fletcher was a regular presenter on Channel 9's weekly football season program "The Footy Show". Fletcher presented the "Kick for Cash" segment.
In 2014, Bryan Fletcher joined Fox Sports "Monday Night with Matty Johns' forming a duo with fellow former NRL player Nathan Hindmarsh. Fletcher and Hindmarsh participate in many challenges set by the producers. 'Fletch & Hindy' created their own spoof NRL bid team known as the 'Nepal Donkeys.'