Bell began his career in 1979 playing for the Manukau Magpies in the Auckland Rugby League competition. In 2011 he was named Manukau's Player of the Century.
Bell then moved to England in August 1982, playing for Carlisle and Leeds over the next two seasons. Dean Bell played left-centre, i.e. number 4, in Leeds' 18-10 victory over Widnes in the 1983–84 John Player Special Trophy Final during the 1983–84 season at Central Park, Wigan on Saturday 14 January 1984. At the end of the 1983/84 season he joined Eastern Suburbs in Australia, playing 42 games for them over the next three seasons. In 1987 Bell was a guest player for the South Island in a match against Auckland. In 1986 he joined Wigan, where he was to experience his greatest success. While at Wigan, Bell became a Seven-time Challenge Cup winner (including three as captain), a Six-time Championship winner, a One-time World Sevens winner, a Five-time John Player Trophy winner, a Two-time Premiership winner and a Four-time Lancashire County Cup winner.
Dean Bell played left-centre, i.e. number 4, in Wigan's 15-8 victory over Oldham in the 1986 Lancashire County Cup Final during the 1986–87 season at Knowsley Road, St. Helens, on Sunday 19 October 1986, was an interchange/substitute in the 28-16 victory over Warrington in the 1987 Lancashire County Cup Final during the 1987–88 season at Knowsley Road, St. Helens, on Sunday 11 October 1987, played left-centre, i.e. number 4, and scored a try in the 22-17 victory over Salford in the 1988 Lancashire County Cup Final during the 1988–89 season at Knowsley Road, St. Helens on Sunday 23 October 1988, and played loose forward/lock in the 5-4 victory over St. Helens in the 1992 Lancashire County Cup Final during the 1992–93 season at Knowsley Road, St. Helens on Sunday 18 October 1992.
Dean Bell played left-centre, i.e. number 4, and scored a try in Wigan's 18-4 victory over Warrington in the 1986–87 John Player Special Trophy Final during the 1986–87 season at Burnden Park, Bolton on Saturday 10 January 1987, played right wing, i.e. number 2, in the 12-6 victory over Widnes in the 1988–89 John Player Special Trophy Final during the 1988–89 season at Burnden Park, Bolton on Saturday 7 January 1989, played left-centre, i.e. number 4, in the 24-12 victory over Halifax in the 1989–90 Regal Trophy Final during the 1988–89 season at Headingley Rugby Stadium, Leeds on Saturday 13 January 1990, and played right-centre, i.e. number 3, in the 15-8 victory over Bradford Northern in the 1992–93 Regal Trophy Final during the 1992–93 season at Elland Road, Leeds on Saturday 23 January 1993.
During the 1992–93 Rugby Football League season Bell played at centre for defending RFL champions Wigan in the 1992 World Club Challenge against the visiting Brisbane Broncos.
Bell also won the Man of Steel Award in 1992 and the Lance Todd Trophy in 1993. Bell was later inducted into the Wigan Warriors Hall of Fame.
In 1994 Bell left Wigan, returning home to join coach John Monie at the new Auckland Warriors club. Bell became the Club's first captain and led the team out in their inaugural match.
During his career he captained Wigan, the Auckland Warriors and the New Zealand national team.
While playing in the Auckland Rugby League competition Bell made the Auckland side. In 1982, he played for Cumbria against Australia during the 1982 Kangaroo tour. A year later, he toured England with the New Zealand Māori team before making his début for New Zealand that same year. In his début match he played alongside his uncle Ian Bell and his cousin Clayton Friend. He went on to play 26 tests for his country, retiring from international football early in 1989.
Bell picked up several honours while playing for his country, including being the NZRL Player of the Year in 1987 and winning the NZ Māori Sports Personality of the Year in 1994. He was later made a member of the NZRL's Immortals and inducted as one of the NZRL's Legends of League in 2000. He is an Auckland Rugby League Immortal.
Bell returned to Leeds in 1996 as coach but ended up playing in one match as player-coach. He remained the first grade coach in 1997 before accepting a two-year job as the head of the Academy team.
During the 2000 World Cup he was the assistant Coach of the Aotearoa Māori side, working under his dad Cameron Bell.
In 2000 he returned to Wigan to head the youth development programme for seven years before being appointed the New Zealand Warriors Development Manager in August 2007.
Bell became the manager for the Warriors Under-20's side in the Toyota Cup and at the end of the 2009 season Bell was promoted by the Warriors to be their new Recruitment and Development Manager.
In 2008 Bell was made the New Zealand Kiwis football manager.
In 2012 Bell was made the New Zealand Vodafone Warriors General Manager Of Football
Bell was also the feature of an episode of the show This is Your Life.