Inspectors have been instructed to take up their duties to investigate Independent News and Media (INM).
The High Court ruled in favour of an application by the State's corporate watchdog to have inspectors examine INM.
INM said it would not appeal against the ruling.
The group's publications include newspapers the Independent and Northern Ireland's Belfast Telegraph.
The Office of the Director of Corporate Enforcement (ODCE) launched the legal bid earlier this year for inspectors to probe governance affairs at the group.
The media company opposed the move on grounds that it could damage its business.
The judge formally approved barrister Sean Gillane and British corporate solicitor Richard Fleck as inspectors at a sitting of the court today, two days after agreeing that inspectors should be appointed.
He had held off making the final order to give INM time to consider his 76-page judgment.
Mr Justice Peter Kelly told the court in Dublin on Thursday that the inspectors could take up their duties effective immediately and that the order he made on Tuesday stood.
The judge awarded all costs to the ODCE against INM.
Senior counsel Sean Gallagher, for INM, said he saw "no grounds" for opposing the costs decision made by Neil Steen for the ODCE.
At a sitting of the court on Tuesday, Mr Justice Peter Kelly rejected the objections of INM's board and said the appointments were in the "public interest" given the dominant position it occupies in the Irish media sector.
The inspectors will investigate whether there may have been alleged unlawful sharing of the company's inside information with third parties outside the company as well as the alleged unlawful sharing of the company's confidential information.
It follows an alleged data breach within the firm in 2014 involving 19 people, including journalists.
INM released a statement today, saying: "The High Court of Ireland has today made an order, in the terms summarised in the Company's announcement of 4 September, appointing Mr Sean Gillane SC and Mr Richard Fleck CBE as inspectors under section 748 of the Companies Act, 2014 to inquire into and report on certain issues relating to the conduct of the affairs of the Company.
"The Company intends to co-operate with the inspectors and assist them in the efficient execution of their inquiry."
In a statement on Tuesday, the inspectors will have at their disposal the wide range of powers provided to them under the Companies Act 2014 and the principal matters to be investigated as indicated by the High Court, include:
• The interrogation of INM’s data;
• The proposed acquisition by INM of Newstalk radio;
• The proposed payment to Island Capital of a success fee associated with the disposal of INM’s shareholding in APN;
• The Independent Review process; and
• Possible breaches of Market Abuse Regulations.