Former CEO of the Rehab group Angela Kerins has lost her legal challenge to the way public hearings were carried out by the Dáil's Public Accounts Committee.
Ms Kerins said two hearings by the Public Accounts Committee into money paid to the Rehab group amounted to a witch-hunt against her.
Her lawyers told the High Court last year she was so overwhelmed by what happened at the first hearing in February 2014, she tried to take her own life two weeks later.
She wanted damages for personal injury, loss of reputation and loss of career.
But her case was rejected by a three-judge division of the High Court.
The court ruled that Ms Kerins was inviting the court to analyse utterances made by Oireachtas members in a Dáil committee and this could not be done.
Giving the court's ruling, Mr Justice Peter Kelly said Ms Kerins claimed what some members of the committee had said amounted to an adjudication or a determination against her.
In reality, however, he said these were clearly just expressions of opinion, devoid of any legal force.
He said under Article 15.13, which protects utterances made by members of the Oireachtas in the house, the court had no power to intervene.
He said Ms Kerins was claiming for damages, seeking to make the TDs amenable to the jurisdiction of the court.
That could not be done. He ruled the court could not analyse, examine, discuss and adjudge utterances made in the Oireachtas.
He said this was not a denial of Ms Kerins' constitutional rights. But the custodian of those rights was the Oireachtas not the court.
He quoted a previous High Court judgment, which found this meant there was a heavier onus on the Oireachtas to ensure constitutional rights were respected.
Mr Justice Kelly said it had been recognised in common law jurisdictions for more than four centuries, that the courts had no function in relation to speech in parliament.
This was fundamental to the separation of powers and was a cornerstone of constitutional democracy.
He said the Constitution guaranteed freedom of speech in parliament not to protect deputies but to protect the democratic process itself.
If members of either house were constrained in the manner contended for by Ms Kerins, he said the effective functioning of parliament would be impaired in a manner forbidden by the constitution.
The judgment may have some bearing on the separate case taken by businessman Denis O'Brien over statements made by two TDs in the Dáil about his banking affairs.
That judgment has been reserved and Ms Justice Úna Ní Raifeartaigh had said she would deliver it after the ruling in Ms Kerins' case.
Ms Kerins' case has been adjourned until 21 February when the issue of costs may be discussed.
She was not in court.
Later, Ms Kerins said she is disappointed after losing her legal challenge. In a statement, she said she was reviewing the judgment with her legal team.
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Sinn Féin TD and member of the Public Accounts Committee Mary Lou McDonald said she was very pleased with the court's ruling.
She said she thought it was the correct conclusion.
She said she very much regretted that Ms Kerins felt moved to take this action but she was very pleased the courts had reasserted the right of elected parliamentarians to carry out their democratic duties.
Ms McDonald said it was important that Oireachtas committees were free to pursue their work unhindered.
She said in the case of the PAC, they dealt with the very serious matters of public monies, of accountability for those monies, of governance and structures.
She said it was absolutely essential that every member of the committee was absolutely free in the public interest to pursue every matter and every question.
She said as elected parliamentarians, it was their special duty to represent the public interest without fear or favour and very vigorously interrogate issues where there was a controversy or a query around the correct use of public monies.
She said the PAC was a tough committee to appear before and the lines of questioning were robust. Although she said it was carried out in a very non-personalised way.
She said she was sorry Ms Kerins had had an episode of ill health.
She said the committee's objective was not to upset or cause distress to anyone.
But she said they did have to follow the money trial and ask the very difficult questions and she was pleased the court had reasserted their right to do just that.
Independent Senator Michael McDowell has described the ruling as "quite significant" and said it makes it "very clear that it's for the Oireachtas itself to determine how it respects people's rights".
Speaking on RTÉ's News at One, the former justice minister said "the determination by the court that utterances in parliament, as they put it, are in an area of non justiciability ordained by the Constitution is a very, very strong finding".
He said "this means that the courts just have no function in relation to condemning, considering, criticising, compensating people for or taking any steps in relation to utterances that are made in parliament".
Mr McDowell said "what the court has said is that it is not a matter for the courts to intervene to put right breaches of constitutional values and rights in the Oireachtas in circumstances as Angela Kerins endured, but it is for the Oireachtas itself to constantly keep those rights in mind as well".