A woman who fell out with her mother stood to gain no part of the £486,000 inheritance, which had been left to various charities, until she successfully contested it under the Inheritance (Provision for Family and Dependants) Act 1975.
The ruling will likely have a huge impact on cases in the future and may mean that many families will bring claims for financial provision from a deceased relative's estate.
Melita Jackson had written a Letter of Wishes that stated she did not want her daughter Heather Ilott to receive any part of her estate, due to a falling out between the two.
Instead, the money was to be given to the RSPCA, RSPB and Blue Cross.
Judges ruled that Mrs Jackson had been "unreasonable" in putting charities before her daughter and awarded Mrs Ilott a share of the inheritance.
This ruling means that people will now have less freedom in making their Wills. It contradicts the Government's recent decision to encourage charitable donations in Wills in the April budget through reducing the Inheritance Tax rate.
Charities could be greatly affected since a large portion of their income comes from gifts of inheritance.
But the new ruling makes it easier for relatives to bring a claim when a Will leaves them unnamed, but instead leaves money to a third sector body or other unrelated parties.
When writing a will, it is always advisable to get support from solicitors and Will writers who will ensure it written clearly and concisely and takes into consideration any potential claims that could be made.