When a loved one's will surprises or unsettles a family, the first question is often: is this will actually valid? Irish law recognises a small number of grounds on which you can question a will's validity. This guide explains each one in plain terms, drawing on the Succession Act 1965 and official guidance, so you can understand your position before deciding what to do next.
This article is an overview of the grounds themselves. For the practical steps, timing, and how a dispute actually proceeds, see our wider guide to contesting a will in Ireland. It sits alongside our guides to finding out what is in a will and the time limits for challenging a will, which matter just as much as the grounds.
The four main grounds at a glance
To challenge a will's validity, you need to show that at least one of the legal requirements for a valid will was not met. The table below summarises the four grounds most commonly used in Ireland. Each is explained in more detail in the sections that follow.
Lack of testamentary capacity
The person did not have the mental capacity to understand the act of making a will, the extent of their estate, or who had a claim on it.
Undue influence
The will was the product of pressure or coercion by another person, so it does not reflect the will-maker's own wishes.
Want of due execution
The will was not signed and witnessed in the way the Succession Act 1965 requires (Section 78).
Suspicious circumstances
The way the will was made raises doubts about whether the will-maker knew and approved its contents.
The main grounds on which a will's validity can be challenged in Ireland. Sources: Succession Act 1965; Citizens Information.
| Ground | What it means |
|---|---|
| Lack of testamentary capacity | The person did not have the mental capacity to understand the act of making a will, the extent of their estate, or who had a claim on it. |
| Undue influence | The will was the product of pressure or coercion by another person, so it does not reflect the will-maker's own wishes. |
| Want of due execution | The will was not signed and witnessed in the way the Succession Act 1965 requires (Section 78). |
| Suspicious circumstances | The way the will was made raises doubts about whether the will-maker knew and approved its contents. |
All four grounds question the validity of the will itself. They are different from a Section 117 claim — where a child argues that a valid will failed to make proper provision for them. That type of claim is about how the estate is divided, not about whether the will is legally valid.
Lack of testamentary capacity
Testamentary capacity is the legal term for the mental capacity needed to make a valid will. According to Citizens Information, you must be able to understand what you are doing and make the decision yourself. Anyone over 18 with that capacity can make a will.
In practice, courts look at whether the will-maker understood three things at the time the will was signed: what it means to make a will and what effect it has, the extent of the property they were leaving, and the people who might reasonably expect to benefit. A challenge on capacity argues the will-maker did not understand one or more of these.
Capacity is assessed at the moment the will was made — not before, and not after. That is why medical records and the recollections of the solicitor and witnesses present are so important as evidence. Citizens Information notes that a person with a condition that could affect their understanding — such as early-stage dementia — can be certified by their doctor as capable at the time. That certification can later help confirm the will was validly made.
Undue influence
Undue influence is where someone pressures or coerces the will-maker so that the will reflects that person's wishes rather than the will-maker's own. The law draws a clear line between ordinary persuasion — which is allowed — and pressure that overpowers the will-maker's free choice. Only the latter counts as undue influence.
Courts look at the surrounding circumstances as a whole. Relevant factors include whether the will-maker was frail, ill, or vulnerable; whether they were dependent on the person who benefited; and whether the will departed sharply from earlier wills by suddenly favouring that person.
You must prove undue influence — it is not assumed. Direct evidence is rare, because coercion usually happens in private. Instead, a case is built from the pattern of circumstances around how the will came to be made.
Want of due execution under Section 78
“Want of due execution” means the will was not signed and witnessed correctly. Section 78 of the Succession Act 1965 sets out the exact formalities required. If those formalities were not followed, the document is not a valid will — no matter how clearly it sets out the will-maker's wishes.
In writing and signed at the end
The will must be signed at the foot or end by the will-maker (or by someone in their presence and at their direction).
Two witnesses present together
The will-maker must make or acknowledge the signature in front of at least two witnesses present at the same time.
Witnesses attest the signature
Each witness must attest and sign the will in the will-maker's presence (the witnesses need not sign in front of each other).
The core execution requirements for a valid will under Section 78 of the Succession Act 1965. Source: Irish Statute Book.
| Requirement | What Section 78 requires |
|---|---|
| In writing and signed at the end | The will must be signed at the foot or end by the will-maker (or by someone in their presence and at their direction). |
| Two witnesses present together | The will-maker must make or acknowledge the signature in front of at least two witnesses present at the same time. |
| Witnesses attest the signature | Each witness must attest and sign the will in the will-maker's presence (the witnesses need not sign in front of each other). |
Section 78 does allow some flexibility on the exact placement of the signature. Under Section 78(3), the signature is sufficient if it is so placed “at or after, or following, or under, or beside, or opposite to the end of the will” that it is apparent the will-maker intended the signature to give effect to the document as their will. Importantly, a signature does not give effect to anything inserted after it was made.
Suspicious circumstances
A will is only valid if the will-maker knew and approved its contents. Once capacity and proper execution are established, this is usually presumed. But where the circumstances raise genuine doubts, that presumption can fall away — and the person relying on the will may have to prove the will-maker understood and approved what it said.
Suspicious circumstances often overlap with undue influence. Typical examples include a will prepared by, or at the instigation of, someone who benefits substantially from it; a sudden change in the will that favours a person close to the will-maker at a vulnerable time; or a will-maker who could not read or was seriously unwell when the will was signed.
Suspicion alone is not enough to set a will aside. What matters is whether the will-maker truly knew and approved the contents. If that can be shown — through clear solicitor's notes and independent witnesses, for example — the will can still stand despite the surrounding doubts.
How a concern about validity is first raised
If you are worried about a will's validity, the most practical first step is usually to stop a grant of probate from being issued while you look into it. The Courts Service allows anyone who intends to oppose a grant to lodge a caveat in the Probate Office or a District Probate Registry.
A caveat prevents a grant of probate or administration from issuing. It lasts six months and can be renewed. It is a holding step that buys you time to investigate — not a challenge to the will in itself, and it does not decide any of the grounds above. Our guide to lodging a caveat in Ireland explains how it works in practice.
Timing matters throughout. Different grounds and claims carry different deadlines, and some are strict. Before relying on any of the grounds in this article, read our guide to the time limits for contesting a will so you do not lose the right to act.
Should you get professional advice?
Challenging a will is one of the more complex areas of probate. The evidence often comes down to medical records, a solicitor's file, and witness recollections from the time the will was made. This article gives a general overview of the grounds — it is not legal advice on your specific situation.
Because the grounds are technical and the time limits are strict, anyone seriously considering a challenge should get legal advice early. A solicitor can assess whether the facts support one of the recognised grounds, give you a realistic view of the prospects, and make sure you act within the relevant deadline. Moving promptly protects your position while the question is examined.