After significant works by the public body alongside Natural England, the Grade I-listed Stray Walls, which lead up to the house, and monuments which dot its landscape, have been removed from the Heritage at Risk Register.
Lime trees which were planted in the 1720s have also been saved.
Eight hundred trees make up the avenue and as part of the work around 60 were felled with 200 more having some form of tree surgery. The look of the avenue will now be re-established following the planting of more than 300 new trees.
More than £300,000 has been put towards restoring parts of Castle Howard by Historic England, and Natural England has invested around £1m alongside funding from the estate itself.
The Stray Walls had received little attention since the eighteenth century and the top of it was crumbling.
The three-quarters-of-a-mile wall was built around 1723 to mark the entrance to the home and emphasise that it was indeed a castle.
Craig McHugh, a principal advisor for Heritage at Risk, said: “They are really visible to visitors as they arrive at Castle Howard – the prominence of the Stray Walls is really critical.
Historic England said Castle Howard, in York, has one of the grandest Baroque landscapes in England.
Nicholas Howard said: “Castle Howard has a rolling conservation deficit of between £40m and £50m.
“The exterior landscape and its buildings are as important as Castle Howard itself, at over 300 years old it is not surprising that their preservation is an ongoing and expensive business.
“The Heritage at Risk Register is a very useful tool in assessing where the priorities lie in this work.
“It is thanks to these bodies, in particular Historic England – and its predecessors such as English Heritage and The Historic Buildings Council – and the income generated from our 250,000 visitors that we have managed to continue to restore these important features in our landscape.
“Between them, the avenues and the stray walls act as an overture to Castle Howard, announcing its presence and preparing the visitor for its exuberance.
“As the new trees take root and the crisp lines of the restored walls cut across the avenue, that overture is heard once more as clearly as the day it was written.”
Mr McHugh said: “It’s a terrific estate and visitor destination for Yorkshire. It’s a really iconic site and is a massive responsibility and undertaking. We are pleased to have helped the estate with that work.”
Several structures remain on the Heritage at Risk Register, including the private family Mausoleum and walled gardens.
Sir John Vanbrugh and Nicholas Hawksmoor designed many of the features at Castle Howard, which many people recognise after it was featured on Granada Television’s 1981 adaption of Evelyn Waugh’s Brideshead Revisited.