Brett this week told BBC Scotland he hoped to have a future with Cowdenbeath but would accept their decision.
And the 24-year-old has now been dismissed by the Central Park club.
This week Brett was also banned by the Scottish FA for four matches, with a further four suspended, for offensive posts on Twitter.
Brett was initially suspended by Cowden as a result of the betting offences, which came to light after the SFA looked at his Twitter account over the alleged offensive tweets.
It was found that he had placed 2,787 bets, with eight of those against his own team, and five of those involving matches in which he played. Players in Scotland are not allowed to bet on any football matches.
Brett had faced a traumatic few years in his personal life, with his 22-year-old wife having died of cancer in January 2015, four months after their daughter Mollie, who was born prematurely, had died.
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Cowdenbeath revealed a club hearing over the betting offences had determined the player was guilty of gross misconduct, and said it was with a "very heavy heart" that the board decided to dismiss the player.
A statement read: "The board's duty was clear. A player betting on his own team to lose, often in matches in which he was playing, is not a situation Cowdenbeath FC could accept or excuse. Simply put, no Cowdenbeath FC player committing such an act could remain in the employ of the club.
"The board of Cowdenbeath FC therefore has today conveyed to Dean its decision is that he is dismissed and his employment has been terminated without notice. We believe this decision to be one that any reasonable employer would make and that it is both fair and reasonable in the circumstances."
The club also revealed that the SFA had found Brett guilty of making "comments upon a social networking site, namely Twitter, that were of a discriminatory, and offensive nature, based upon sexual orientation as well as comments that were otherwise of an offensive nature," resulting in the ban.
Cowdenbeath defender Dean Brett has been sacked by the League Two club after admitting betting against his own team.