Knole House in Sevenoaks, Kent, is to receive £7.75m for repairs and conservation from the Heritage Lottery Fund.
The funding will also go towards the construction of new visitor facilities at the 15th century medieval palace, a former hunting lodge to Henry VIII.
The National Trust said that since acquiring Knole in 1946, it had faced expensive running battles with rain, damp, mould and insects, but the funding meant the future of the mansion and its treasures were now secure.
More top news
A mum from Essex has launched a campaign to encourage young black women to stop altering their natural hair.
Arthur Simpson-Kent killed Sian Blake and their sons at their bungalow in Erith, south-east London.
Samples from 95 buildings in 32 local authority areas have failed fire safety tests - 100% of the cladding samples submitted.