One of the New South Wales Southern Highlands' grandest historic properties has been gifted to the National Trust of Australia.

Philanthropist and arts patron James Fairfax has gifted Retford Park to the trust, along with a multi-million-dollar endowment to maintain and conserve the 33ha Bowral property.

Retford Park has been the country home of the former chairman and director of Fairfax Limited since he acquired it as a 4ha holding in 1964.

National Trust CEO Brian Scarsbrick said it was the largest gift to the organisation's NSW division in its 70-year history.

"This gift from James Fairfax is one that is a real knockout. The property is worth around $20 million," Mr Scarsbrick said.

"This will be a real showcase and it's one of the first National Trust heritage properties that you come across when you drive from Sydney to the Southern Highlands."

Speaking at a handover ceremony at Retford Park on Tuesday, Mr Fairfax said it had long been his wish that the property be preserved.

"So that future generations can see how the property was lived in and used," he said.

"I know that I am transferring the property into safe hands to be preserved for future generations of Australians."

While the National Trust is the new owner of the property, it has leased it back to Mr Fairfax for the duration of his lifetime.

It is a condition of the lease that the public be able to view Retford House.

Property will form part of heritage trail

The property will be open to the public occasionally, but a date for the first time it will open its doors to visitors is yet to be set.

Retford Park will form part of a heritage property trail through the Southern Highlands.

National Trust president Clive Lucas said it would be the first and grandest heritage property on the National Trust Heritage Trail, which would run along the Old Hume Highway.

"Ultimately, heritage enthusiasts will be able to visit Retford Park at Bowral, Harper's Mansion at Berrima, Golden Vale at Sutton Forrest, Riversdale at Goulburn, and Cooma Cottage at Yass as part of a package tour," Dr Lucas said.

Since acquiring Retford Park in 1964 for £15,000, Mr Fairfax has over time increased the holding to 120ha, changing it to suit his tastes.

"While the drive and garden was overgrown, the house itself was in fairly good order," his financial advisor, Allen Robinson, told the ABC's PM program.

"But [it] wasn't decorated in his taste. He had Lesley Walford come in and redecorate it in a style that suited."

Ninety hectares on the eastern and western sides is now being developed for new homes.

The National Trust said a significant portion of the sale proceeds from the housing development also would be gifted to its heritage foundation to provide income for the ongoing upkeep and maintenance of the property.

Mr Robinson has been working for years on a plan to make the historic building available to the public.

"After research and lots of discussions we decided the national trust would be a suitable owner," he said.

An aerial photo of Retford Park, the country home and its surrounding stables and grounds. ( Supplied: National Trust of Australia )

Rich history dates back to 1821

According to the website for Retford Park, European ownership of the land on which it is situated dates from 1821, when Governor Macquarie granted Edward Riley two parcels of land originally named Bloomfield.

The property remained in the Riley family until the 1880s when it was acquired by Samuel Hordern, son of Anthony Hordern, who renamed it Retford Park in recognition of family links to Retford in Nottinghamshire, England.

The house was completed in 1887 and included horse and cattle facilities.

The last Hordern resident, Samuel Hordern III, died in a car crash in 1960 before an American-owned company, King Ranch, briefly owned the property.

Mr Fairfax bought the house from King Ranch in 1964 and redecorated it, along with renovating the garden under advice from renowned architects.

The country home has played host to members of the British and European royal families.