Sean Quinn Junior has been awarded more than €95,000 after an Employment Appeals Tribunal determined he had been sacked by his former employers "under the cloak of redundancy".
The son of the country's one-time richest man, Sean Quinn, had alleged that he was dismissed from his role as head of claims with Quinn Insurance as part of a "de-Quinning" process at the company.
In a ruling by the EAT, published on May 20, the tribunal said the company had not acted fairly and that the dismissal had "lacked the impersonality" associated with redundancies.
The victory for Sean Quinn Junior comes as he, his sisters Aoife, Ciara, Colette and Brenda, and their mother Patricia prepare for a €4.3bn legal action against the former Anglo Irish Bank in the High Court this week.
The employment case against Quinn Insurance was brought after joint administrators were appointed to the firm following a request by the Central Bank after the financial regulator had raised concerns about the business in March 2010.
The company had argued that Mr Quinn had lost his job because the role he had filled had ceased to exist.
However, Mr Quinn, who was imprisoned in 2012 for contempt of court, made a number of allegations against his former employers during several days of hearings earlier this year and last year.
The tribunal heard he had his access to the company's computer system disabled and that he felt he was being "victimised".
He also alleged that he had been instructed not to attend any meetings of senior management. He said he and his siblings had been targeted and he was advised to take redundancy.
The tribunal also heard testimony that at one particular meeting Michael McAteer, of administrators Grant Thornton, had identified staff members who were close with Sean Quinn Jnr and advised them not to associate with him.
This was denied by Mr McAteer when he gave evidence, and he also rejected the claim he told Mr Quinn to leave the company. However, the tribunal ruled that it was relevant that Mr McAteer accepted he "possibly" disabled Mr Quinn's IT access.
Giving its determination, the Tribunal said it was "not satisfied" that there was a genuine redundancy and said the claimant had been let go from the firm "under the cloak of redundancy".
"The tribunal is satisfied that the respondent did not act fairly and reasonably in his dealings with the claimant," the tribunal said.
"There was a fractious relationship between the claimant and the respondent and the dismissal lacked the impersonality associated with redundancy," it said.
It added: "The tribunal is satisfied that the claimant was dismissed for matters other than redundancy under the cloak of redundancy."
Sean Quinn Junior told the tribunal he was unemployed.
At one stage he owned 20pc of the Quinn Group - the vast business empire built up by his father.
He married his partner Karen Woods in 2012 during his contempt of court proceedings and served three months in jail after he failed to comply with court orders to reverse steps to put international assets out of the reach of the now liquidated IBRC, which was formerly known as Anglo Irish Bank.
The family's High Court case, which is expected to begin on Wednesday, will see the Quinns claim that €2.3bn in loans that were extended to various Quinn companies were illegal.
The bank is accusing the family of attempting to put assets beyond its reach.