He was involved in one of the most publicized incidents of on-ice violence in NHL history during the 1999–2000 season, when he was slashed in the head by Marty McSorley.

[3] Donald's mother later stated that she left him behind because her future husband was prejudiced and wanted to avoid having another mixed-race child in the house.

[3] To help pay for hockey, Brashear sold baked bread and garbage bags door-to-door, and later became a paper boy.

[5] He spent parts of three seasons with their American Hockey League (AHL) affiliate, the Fredericton Canadiens, before becoming a regular with Montreal at the NHL level.

During the 1993–94 AHL season, he registered professional career highs of 38 goals and 66 points, along with 250 Penalty Minutes (PIMs) in 62 games.

[8] After playing parts of four seasons with the Canadiens, his time in Montreal ended following a heated verbal exchange with Head Coach Mario Tremblay during a team practice[5] on November 9, 1996.

[6][11] The following season, 1997–98, Brashear led the NHL in penalty minutes and set a Canucks franchise record with 372 PIMs,[12][13] while adding 18 points.

[14] The 1998–99 season marked the only time in his career which he played in all 82 games, again leading the Canucks in penalty minutes and finishing eighth in the NHL.

[19] With 4.6 seconds left in the game,[20] a frustrated McSorley finally swung his stick toward Brashear's head from behind and struck him with a two-handed slash to the right temple.

The fight was believed to be in retaliation to Flyers forward Mark Recchi being slashed in the face by the Senators Martin Havlát.

[33] He registered 18 goals and 50 points in 47 games,[6] but was reluctant to fight and felt the League did little to protect him from players wanting to make a name for themselves against an established NHL enforcer.

[33] Following the lockout, Brashear voiced his displeasure with the new way the League called games, stating that the NHL changed the rules to favor "superstars," and he felt that there was no longer a way to "get respect" on the ice.

[36] At the end of the year, he was again in the top ten (eighth) in PIMs, accumulating 166,[37] but his offensive production dropped to a mere nine points.

[40] He was suspended one game by the NHL during the regular season for punching New York Rangers defenceman Aaron Ward following a fight between Brashear and Brendan Shanahan.

In the pre-game warm-ups, Brashear shoved Rangers enforcer Colton Orr, then delivered a blind-side hit to Blair Betts mid-way through the game's first period.

[47] Colin Campbell ruled that the hit was late on an unsuspecting player; he also believed it targeted the head, and as a result caused significant injury.

[48] Brashear was not given an extension during the season, and before the start of the free agency, he indicated that he would like to return to Washington, citing the prospect of winning a Stanley Cup.

Brashear noted that at his age and place in his career, taking care of his family was his top priority and that money would be the deciding factor in his destination.

After initial talks with the Kontinental Hockey League (KHL)'s Vityaz Chekhov, he eventually agreed to a two-year, $2.8 million contract with the New York Rangers.

[57] Instead of buying-out his contract, however, the Rangers traded Brashear on August 2, 2010, along with Patrick Rissmiller, to the Atlanta Thrashers in exchange for centre Todd White.

[58] Atlanta then placed Brashear on waivers and bought-out the remaining year of his contract, thus making him an unrestricted free agent.

He made his international debut at the 1997 World Championship, where he registered two goals and five points in eight games,[67] helping the Americans to a sixth-place finish.

"[5] Brashear was a tenacious forechecker,[39] who created momentum by playing aggressively and delivering body checks,[69][70] while possessing an underrated shot.

[5] Whilst fighting, he used a combination of balance and upper-body strength while taking his time trying to control his opponents before landing punches.

"[74] Hockey analyst Bill Clement states that "Brashear has a great sense of when his fighting skills are necessary and he picks his spots before dropping the gloves.

"[71] The Hockey News also assessed his skills by saying he possessed one of the most intimidating packages in the League, had a decent skating stride, and was one of the best pugilists in the NHL.

"That's no way to show my boys how to solve their problems", Brashear said after the guilty verdict, also lamenting the fact that he had trouble controlling a violent temper inherited from his father.

Later on, he trained with former heavyweight champion Smokin' Joe Frazier[81] In 2007, Brashear, along with some friends, founded the house building company DEC Construction.

[82] In 2012, Brashear was convicted of assault for a second time after an altercation in a parking lot following a March 2011, Ligue Nord-Américaine de Hockey playoff game.

[84] In October 2019, it was reported that Brashear was working at a Tim Hortons restaurant in Quebec City owned by Pierre Sévigny.