The Irish Heritage Trust is to take over responsibility for Fota House in Co Cork from September. It is the first acquisition by the new body.
For the past 14 years, the house has been managed by the Fota Trust, which was established by University College Cork (UCC) represented by Prof Tom Raftery, Cork City Council and Cork County Council.
The extensive arboretum and gardens are in the care of the Office of Public Works (OPW).
The Irish Heritage Trust was formally established in July last year, and Fota House is the first acquisition under its mandate to acquire properties of significant heritage value, "where there is a risk to such value", and to provide the necessary conservation, maintenance and preservation of such properties.
The decision to take over Fota has been welcomed by David Bird, chairman of the Fota Trust, who said yesterday it had been understood that this was the most likely outcome of Fota's application to the Department of the Environment, Heritage and Local Government for assistance with the management of the historic property.
Once the centrepiece of the Smith-Barry estate near Cobh, Co Cork, the house has most recently been partially restored by the OPW at a cost of €4.5 million, and costs at least €200,000 a year to run.
Originally a hunting lodge, it was redesigned by Cork-born architect Sir Richard Morrison and his son Vitruvius in 1820 and was sold with the estate to UCC in 1975.
While in the hands of UCC, the house was restored as a small museum by Cork businessman Richard Wood, who hung his collection of Irish landscape paintings there until the sale of the property by the university.
Now much of the island estate is taken up by a golf course and clubhouse accompanying the Sheraton Fota hotel, as well as a housing scheme in the surrounding woodland.
Fota Wildlife Park is a separate entity managed by the Royal Zoological Society.
The Irish Heritage Trust, which is required to ensure the public enjoyment of such properties and public access "in perpetuity", expects to acquire the garden in five years' time.
While there is a fee for entry to the house, the garden has been open to the public free of charge since before it was taken into the care of the OPW.
Planned as a self-sustaining organisation, the new trust has been given an initial three-year grant by the department.
The trust chairman, Sir David Davies, and the board are to meet at Fota next month. A local committee is expected to be set up under a director who has yet to be appointed. A management review will be undertaken but no staffing changes are expected.