Nicola Stocker wrote that Ronald Stocker tried to strangle her, during an online exchange with his new partner in 2012.
She was left facing a legal bill of about £300,000 after Mr Stocker successfully sued her at the High Court for defamation - a decision which was upheld by the Court of Appeal.
But, after she took her case to the Supreme Court, the previous rulings were overturned by a panel of five justices on Wednesday.
Mrs Stocker, 51, of Longwick, Buckinghamshire, said: “I am just delighted, hugely relieved.
“I think it highlights the danger that the courts are being used by men to continue an abusive process, whether it be in the family courts or through a libel court.
“If they have got the money to do it, they will. It has been five years of my life that has been hell.
“The emotional and financial damage that it does is huge.”
Mr Stocker, 68, of Aston Clinton, Buckinghamshire, originally won his legal action against his ex-wife at the High Court in London, after Mr Justice Mitting found that those reading the comments would think she meant he had “tried to kill” her.
However, announcing the Supreme Court’s ruling in London on Wednesday, Lord Kerr said the judge made a “legal error” by relying on the dictionary definition of “strangle”.
He said Mr Justice Mitting’s approach to the case “illustrates the danger” of using dictionary definitions as a guide to the meaning of an alleged defamatory statement.
Lord Kerr also said the fact that the comments were made on Facebook was “critical” and that any assessment of such posts should reflect the conversational nature of the “casual medium”.
He added: “We have concluded that, knowing that Mrs Stocker was alive, an ordinary reader of Facebook would have interpreted those words to mean that Mr Stocker had grasped his wife by the throat and applied force to her neck, rather than that he had tried to kill her.”
During the High Court trial in 2016, the court heard that the allegations were published to 21 individuals who had authorised access to the Facebook profile of Mr Stocker’s new partner, Deborah Bligh.
They were also visible to 110 of Ms Bligh’s “friends” and to their Facebook “friends”.
Ruling in Mrs Stocker’s favour and ordering Mr Stocker to pay all legal costs, Lord Kerr said: “It is beyond dispute that Mr Stocker grasped his wife by the throat so tightly as to leave red marks on her neck visible to police officers two hours after the attack on her took place.
“It is not disputed that he breached a non-molestation order. Nor has it been asserted that he did not utter threats to Mrs Stocker.
“Many would consider these to be sufficient to establish that he was a dangerous and disreputable man.”
Solicitor advocate David Price QC, who represented Mrs Stocker, said: “I’m delighted for Nicola that she has finally got some common sense and justice, albeit five and a half years after the process started and having to go to the Supreme Court.”
He added: “It does take a unique person who is willing and has the courage to fight it.”
Mr Price said current libel laws make it “difficult, if not impossible” for an ordinary person to defend themselves against a claim due to the cost and complexity.
Harriet Wistrich of the Centre for Women’s Justice (CWJ), which supported Mrs Stocker’s appeal, said: “We have been supporting this case and a number of others because essentially what these cases do is enable wealthy men to try to silence women through the libel laws.
“Strangulation, whether or not someone is meaning to kill, is a very dangerous act.”