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 24-year-old man has appeared in court this morning after a fatal hit-and-run of a 58-year-old man in east London.
Fifty people had to be evacuated from a three storey block of flats after fire broke out in its roof.
Two people had their lives saved by a smoke alarm after fire ripped through their house in south west London.