Declan Gormley, the sacked former director of Northern Ireland Water, sued the party and two of its officials – MLA Cathal Boylan and former Assemblyman Willie Clarke.
Sinn Fein was sued over the contents of press releases that referred to Mr Gormley's March 2010 dismissal from the government-owned company by Conor Murphy, the former Sinn Fein minister for regional development.
The party denied the press releases were defamatory, but last Friday a jury found the party had acted with malice.
Last night Mr Gormley, who was awarded £80,000 (€98,000) in damages, said Sinn Fein had refused repeated efforts to settle the case with a public apology.
On top of the compensation, Sinn Fein is facing legal costs estimated to exceed £400,000 (€492,000).
"I feel relieved and totally vindicated," Mr Gormley told the Irish Independent.
"I was happy to settle for an acknowledgment (by Sinn Fein) that they were wrong. I was willing to negotiate an agreement that would have satisfied both parties, but they wouldn't."
Mr Gormley insisted that the case was "never about money".
"It was difficult, but I was determined to see it through," said Mr Gormley who was dismissed, along with three other non-executive directors, from NI Water, in March 2010.
Mr Murphy, then Regional Development Minister, removed them from the board following an independent review team investigation into the awarding of contracts.
A subsequent Stormont Public Accounts Committee report was said to have criticised the earlier inquiry and questioned its independence.
Mr Gormley emphatically denied any wrongdoing.
During the hearing, Mr Gormley's legal team claimed they damaged his reputation and were reckless, if not dishonest.
But Sinn Fein contended that neither statement contained any defamatory content. They also claimed a defence of qualified privilege, arguing that the press releases were in response to a campaign of attacks on Mr Murphy mounted by the SDLP with Mr Gormley's collusion.