The Landmark Trust has funding for Llwyn Celyn farmhouse in Monmouthshire, with the aim of restoring its 500-plus years of architectural legacy.
The Grade 1 Listed medieval hall house is considered the most significant inhabited "at risk" building in Wales.
Welsh heritage body Cadw and the National Heritage Memorial Fund (NHMF) gave grants totalling Â£670,000.
Thought to date from around 1480, the property is said to represent key developments in Welsh architecture between the 15th and 18th Centuries and a textbook example of the development of the British manor house.
Largely untouched for the past century, the house is in more than six acres (2.6 hectares) of ground, near Llanvihangel Crucorney in the Llanthony Valley, and still has smoke-blackened roofs from its early years - the chimneys and floors were added in the 17th Century.
Jennifer Stewart, of the NHMF, said the aim of the work was to "build up the story and the story book of who lived in the property at different stages".
She said: "Because it has been in private hands for 100 years, we really don't know that much about it.
"Unlike modern houses, we don't know what is behind the panelling. We want to see what this house is like inside and what it was like to live in this house. There's a huge amount to be discovered there."
However, it is thought that the original owner must have been someone of considerable status and wealth and there is possibly a connection with Llanthony Priory which is situated less than six miles away.
The Landmark Trust is to begin fundraising for the restoration and the house, which sits within the Brecon Beacons National Park, will be available for rent as holiday accommodation.
SOURCE: Cadw
Ms Stewart added: "Often the way to preserve [buildings like this] is to find them a use. This is an other way to find a modern use for an ancient building.
"This is helping the building to "breathe" if you like. If people have enjoyed their stay, they may well provide additional funds."
Peter Pearce, director of the Landmark Trust, said: "The importance of Llwyn Celyn in helping us understand the development of high status Welsh houses more fully cannot be understated."

The explosion happened at about 00:40 GMT on Sunday at a car dealership on the city's Cathedral Road.
Houses in the area were evacuated while army bomb experts searched the scene and examined the device.
Police said they believed the bomb was left at the dealership by a person carrying a backpack 10 minutes before it detonated.
Det Insp Will Tate said: "Today we are lucky that we are not dealing with a serious injury caused by this device and the reckless actions of the person or people behind it."
The security alert has ended and residents have been allowed to return to their homes.
Roads that were closed during the alert have now reopened, apart from a small section of the Cathedral Road.

Express Wi-fi allows users to purchase data from local providers in order to access the web.
A pilot version with a state-run telecoms company has already been offered at 125 rural wi-fi hotspots.
In a statement, Facebook said the tests were being carried out with "multiple local ISP partners".
Facebook is probably hoping that users who first encounter the web via a Facebook initiative will be more likely to become users of the social network - rather than a competitor - according to Ian Fogg, an analyst at IHS Technology.
"In emerging economies, Facebook is pursuing an intervention strategy to increase the pace of internet and online usage because this will also raise the addressable market for Facebook," he told the BBC.
Earlier this year, Facebook's Free Basics internet service app was blocked by India's telecoms regulator.
A ruling in favour of net neutrality put a stop to the plans, which would have offered free access to a select number of websites only.
It may not look like much now, but this in-need-of-attention property is set to be a holiday let for history fans.
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A pipe bomb blast has caused damage to four vehicles in Armagh, police have said.
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Facebook has confirmed that it is in the early stages of testing a wi-fi service with Indian internet service providers (ISPs).