Kennedy, who is 44, made the announcement yesterday afternoon, after telephoning fellow congressmen and political allies to inform them of his decision.
From being almost a foregone conclusion at the beginning of this year, Joseph Kennedy II's election to the governship had turned into an uphill struggle in a matter of months, after a series of scandals that refused to die down. Earlier this year, his ex-wife, Sheila Rauch Kennedy, published a book in which she bitterly attacked him for annulling their marriage without her agreement. and took the Catholic Church to task for the whole practice of annulment.
At the same time, Joe Kennedy's younger, married brother, Michael, was investigated for allegedly having a three-year affair with the family's underage baby-sitter.
The case was kept out of the courts when the family of the girl concerned, now a college student and of age, decided not to proceed, and the police dropped the case. Michael Kennedy, however, never denied the allegations, which left the impression of a law-breaker getting away with it because he was a Kennedy.
Joe and Michael are sons of the late Senator Robert Kennedy, who was assassinated in 1968, less than five years after his brother.
Earlier this month, John Kennedy Jr, son of the late president, used an article in George, the New York magazine he founded, to criticise the conduct of his cousins.
Dubbing them "poster boys for bad behaviour", he said: "great privilege demands great responsibilities." His words were seen as an unprecedented breach in the Kennedy family's traditionally cast-iron solidarity.
Joe Kennedy's decision not to seek the governorship of Massachussetts, a state in which Kennedys have stood for elected posts 18 times in the past half-century without once losing, suggests an acceptance that his chances of winning were slim. Polls had shown a dramatic slide in his popularity to only 34 per cent, following the recent scandals.
Mary Dejevsky, Washington