Knight Frank partner Robert Dixon, who is managing the sale, said it was a rare opportunity for the right buyer.

"This will be marketed locally, nationally and internationally, and we're expecting that there will be interest from all three sectors," he said.

"Cullenswood provides an outstanding and unique opportunity.

"It possesses all the fundamental attributes agri-investors are now seeking."

The 2590-hectare estate is being used for pastoral grazing.

However, it would be ideal for intensive agriculture, Mr Dixon said.

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It traditionally gets 900mm of rainfall a year.

"The attributes that it has are water and further water potential, which are key drivers for intensive agriculture," Mr Dixon said.

"It's been used for more traditional grazing purposes, but with the water you've got dairying opportunities, livestock fattening opportunities, and cropping opportunities."

He also mentioned timber plantations, farm storage and passive mining royalties as potential sources of profit from the property.

Cullenswood is about five minutes' drive from the town of St Marys.

It has been owned by the same family for six generations, the Legge family.

Past owners include former Break O'Day mayor Robert Legge, and Colonel William Vincent Legge.

William Cinvent Legge was born at the property on September 2, 1841, and died there on March 25, 1918.

He was an Australian soldier and an ornithologist who documented the birds of Sri Lanka

Legge's hawk-eagle is named after him as is Legges Tor, the second highest peak in Tasmania.

The main homestead of Cullenswood, which was nine bedrooms, was built in 1827 using convict labour.

A church on the property was built in the 1847, also by convicts.

The gardens feature some of the largest redwood trees in the Southern Hemisphere.

Mr Dixon said there was no reason for the sale besides that "the family have made the decision to sell".

The marketing campaign for the sale process for the property will begin on Thursday.