Robert F Kennedy Jr accused his wife Mary of being physically abusive and asked a court to protect him and his children from her, according to newly revealed legal papers.
The couple were estranged, with a divorce case pending, when Mary Kennedy committed suicide last month at the family's estate in Bedford, New York.
The nephew of JFK married Mary in 1994 and the couple had four children together.
The confidential affidavit was filed in 2011 as part of the divorce proceedings, but excerpts have just been posted online by The Daily Beast news site.
In the filing, Mr Kennedy accuses his wife of abusing his two children from an earlier marriage, running over and killing the family dog, stealing items from his younger daughter, calling him dozens of times a day and turning up uninvited on trips after they split up.
He describes various occasions when his wife, a trained boxer, lashed out at him, at one point giving him a black eye and crushing his tear duct with her engagement ring, causing permanent damage.
He wrote: "Mary's violence and physical abuse toward me began before we were married."
He asks the court that Mrs Kennedy be required to remain sober in the company of their children, and not to talk about suicide in front of them.
In the affidavit he described her as "kind, generous" and "stunningly beautiful", but that her behaviour became "particularly hateful" towards his younger daughter by his first marriage.
The nine-year-old girl would often lose things like her wallet or plane tickets, and Mr Kennedy got irritated with her about it.
But one day, he wrote, his daughter turned to him and said his second wife was stealing things from her.
When he tried to convince his child this could not be true, he wrote: "She looked me in the eye and said, 'no daddy, Mary hates me.'"
Weeks later, he said he found the items hidden in a drawer under his wife's clothes.
Mr Kennedy asked the court for a protective order and a child custody agreement "for the sake of my children and for my own safety and sanity".
Mary Kennedy's private turmoil became public once her husband filed for divorce in 2010.
She was twice charged with drink driving.
Speaking about her death, her sister Kerry said: "She struggled so hard, for so long, with mental illness, which so many Americans suffer with.
"She fought with dignity, and in the end, the demons won."