You might choose to challenge the legal validity of a will if:

• the will was not properly signed and witnessed (see: “Is my will valid?”)
• the deceased did not have full mental capacity (which means they were not able to make and understand decisions for themselves) when they signed the will
• the deceased did not know what was in the will when they signed it
• someone else fraudulently wrote or changed the will, or took advantage of the deceased and excessively influenced or coerced them to change the will.

Wills Act 2007, s 14

You have to go to the High Court to challenge the legal validity of a will. This is a complex process and usually requires the help of a lawyer.

As soon as you decide to challenge a will, you should file a warning (called a “caveat”) with the High Court. This means that when the executor/administrator applies to the High Court for probate of the will, they are required to notify you and serve you copies of the documents. You then become respondent to the application for probate and can file documents with the court to argue that the will is legally invalid.

You need to make sure to file this caveat before probate is granted. Technically, a court could declare a will invalid after granting probate, but it would be a much more difficult process, and some of the estate might have already been distributed.

Note: Even if a will doesn’t meet all the formal requirements for a valid will (for example, to have two witnesses), the High Court has a broad power to approve the will so long as the judge agrees that it expresses the deceased’s intentions.

If the High Court decides that the will is invalid, it means:

• that will is thrown out entirely, and:
• any earlier will of the deceased is reinstated, or
• if there is no earlier will, the deceased’s property will be dealt with under the laws of intestacy (see: “Who gets the property if there’s no will?”).