Brendan Witt was drafted in the 1st round, 11th overall, in the 1993 NHL Entry Draft by the Washington Capitals. The Humboldt, Saskatchewan native played his first major junior game in the 1991 WHL playoffs with the Seattle Thunderbirds. The following season, he scored 12 points as a WHL rookie. In 1992-93, Witt improved to 28 points and was named a WHL West First Team All-Star. In 1993-94, he scored 39 points in 56 games and was named both a WHL West First Team All-Star and a CHL First Team All-Star.
In October, 1995, Witt made his NHL debut and on October 26 scored his first NHL goal against the Boston Bruins. The following season, he played 44 games with the Capitals. In 1997-98, Witt played 64 games and scored eight points. In the playoffs, he helped his team win the Prince of Wales Trophy in the Eastern Conference finals before losing to the Red Wings in the Stanley Cup finals. In 1999-00, Witt played in 77 games and had an impressive 105 blocked shots as the Capitals won the Southeast Division title. In 2000-01, Witt led the Capitals with 207 hits as the team won its second straight Southeast Division title. A defensive minded defenceman, Witt continued his strong play in 2001-02 and went on to play parts of ten seasons with the Caps before having his rights acquired by the Nashville Predators at the 2006 NHL trade deadline.
After only 17 games with the Predators, Witt was signed as a free agent with the New York Islanders in the summer of 2006. In his first full season, Witt patrolled the Islander blue line in 81 games and made his presence felt night in, night out. In 2007-08 he suffered a strain of injuries to his knee, but managed to appear in 59 games.
On the international stage, Witt won a gold medal with Canada at the 1993 World Junior Championships.