Minister for Health James Reilly has announced that the Government has approved the cystic fibrosis drug Kalydeco for use in Ireland from 1 March.
The National Centre for Pharmacoeconomics recently recommended against its sanction for use at a cost of more than €234,000 per patient per year.
Further discussions with the manufactures have resulted in significant savings in the cost.
The drug can lead to significant improvements for patients with a particular mutation of cystic fibrosis.
It is understood that around 120 people will benefit from the announcement. The drug will cost in excess of €20m per annum.
The minister said the terms of the deal with Kalydeco's manufacturer, Vertex Pharmaceuticals, would remain confidential.
He said the performance of the drug will be closely monitored to ensure that the results promised by the company are delivered on.
Mr Reilly said that such is the scale of the spend on the drug that the HSE, who would normally make the decision, passed it up to him for a policy decision.
He added: "I had a phone call with the Taoiseach this morning to discuss this, I also discussed it with (Minister of State) Kathleen Lynch and we are absolutely clear that this drug must be made available to the 120 people who have that genome type and can benefit from it."
Cystic fibrosis sufferer and campaigner Orla Tinsley has said the new drug offered great hope for people with the illness.
Speaking on RTE's Six-One News, Ms Tinsley said it was the first drug for CF that treated the cause instead of just the symptoms.
She acknowledged that Kalydeco is extremely expensive, but said it is worth it for the changes it makes to people's lives.
Cystic Fibrosis Ireland Chief Executive Phillip Watt welcomed the announcement that Kalydeco will be made available in Ireland.
He said it was a groundbreaking drug and described the decision as a "very important day in the history of CF care in Ireland".
Speaking on RTÉ's Drivetime, Mr Watt said the particular strain that the drug treats affects 10% of all CF sufferers in Ireland and was more common in the southwest of the country.
He said the science behind the drug offered hope to its members.
The decision has also been welcomed by Fianna Fáil health spokesperson Billy Kelleher.
He said: "This will go a long way to ease the anxiety of CF patients, who are waiting weeks for this announcement.
"Their quality of life will now hopefully be vastly improved as a result of receiving Kalydeco."