Greenway, a 278-acre estate on the banks of the river Dart, near Dartmouth in Devon, is currently lived in by Christie's only daughter, Rosalind Hicks, and will be given to the Trust after her death.
The house, which Christie bought in 1938, was the setting for several of the author's books and she also used it as a summer retreat.
Mathew Prichard, Christie's grandson, said: "We very much hope that the National Trust, with all its history and experience of looking after other great properties, will be able to take on the responsibility of Greenway. If all goes according to plan, we hope that Greenway will be changed as little as possible."
A National Trust spokeswoman said there were no plans at present to open the house to the public but the gardens would be restored and available to view. "We need pounds 1.1m to restore it and also planning permission which we are applying for. The gardens were fabulous in Agatha Christie's time and she was a very keen gardener but they have been neglected and we need to restore them.
"At the moment there are no plans to open the house up but because it is being handed over to us that will prevent it from being bought by a property developer and turned into some sort of themed hotel."
Greenway was built in the 1790s and the estate includes a farm, woodland and river frontage, a 32-acre garden as well as several listed buildings including a bathhouse and boathouse.
Christie, who is still one of Britain's most popular thriller writers, was born in Torquay in 1890. She published her first detective novel The Mysterious Affair at Styles - introducing the eccentric and egotistic Belgian detective Hercule Poirot - in 1920. At the time she was working as a nurse and had become fascinated by poison.
In 1926 she won major recognition with The Murder of Roger Ackroyd and four years later Jane Marple, the spinsterly detective, made her debut.
She had one child, Rosalind, from her first marriage to Archibald Christie whom she divorced in 1928. Two years later she married Sir Max Mallowan, an archaeologist of whom she said: "The great advantage of being married to an archaeologist is the older you get, the more interested he becomes in you."
Rosalind had one son, Mr Prichard, who has agreed with his mother that the house should be given to the Trust.
He remembers spending summer holidays at Greenway and looks after his grandmother's copyright. "It was an idyllic atmosphere for a kid of six ... and it's a part of my life that I shall never forget. And there were usually members of the literary profession, publishers and Peter Sanders, who was the producer of The Mousetrap, and my step-grandfather's archaeological friends."
The estate, which covers a important section of the Dart estuary, will also be a big contribution to the Trust's Neptune Coastline Campaign, which is working to protect the coastline of England, Wales and Northern Ireland.Reuse content