Mutual Wills: A Doctrine Every Estate Planner Should Understand

Authored by Radhia Razali

An Overlooked Feature of Probate Law

Most people assume a will can always be changed. As a matter of pure probate law, that is generally true; a will is ambulatory and can be revoked or replaced at any time before death. But Malaysian law recognises an important exception: the doctrine of mutual wills. Where two people agree to make wills in matching terms on the understanding that neither will depart from the arrangement, that agreement can bind the survivor even after the other has died, regardless of what a later will says. A recent Court of Appeal decision, Charanjeet Kaur a/p Sukhbir Singh v Zhao Jingkun and another appeal [2025] MLJU 5032, illustrates how the doctrine works and how easily it can be missed at trial.

What Is a Mutual Will?

A mutual will is not simply a will that mirrors another person's will in its terms. Mirror wills, commonly made by spouses who each leave everything to the other and then to the same beneficiaries, are freely revocable by either party at any time, even after the other has died. A mutual will is different. It requires a prior agreement between the makers that their wills are to become irrevocable once one of them dies, and that the survivor will carry the agreed arrangement into effect. The Court of Appeal, citing the High Court's earlier decision in Hiroto Watanabe v Law Yen Yen & Anor [2012] 8 MLJ 202, confirmed that two elements must be established: a prior agreement to make mutual wills intended to become irrevocable on the first death, and the actual making of wills pursuant to that agreement.

Once the first party dies without having revoked the arrangement, equity intervenes. The survivor becomes a constructive trustee of the relevant property, holding it in trust for the beneficiary the parties originally agreed upon. A later will made by the survivor may still be valid as a testamentary document, but it cannot defeat the beneficial interest already attached to the property.

How the Doctrine Played Out in Charanjeet Kaur

The deceased and his first wife, married for 29 years without children, treated their niece as a daughter and executed matching wills in 2007 leaving their jointly owned home to her. After the first wife died in 2008, the deceased remarried in 2012 and, in 2014, executed a new will leaving the same house to his second wife. Following his death in 2019, the executor of the 2007 wills sought to enforce the original arrangement, while the second wife sought probate of the 2014 will.

The High Court held that the 2007 wills were not mutual, largely because there was no documentary record of instructions to prepare mutual wills and because the wills did not use the word “irrevocable.” The Court of Appeal reversed that finding. It held that the absence of written instructions was not fatal where the drafting lawyer was a close family friend acting without charge, and that corroborating testimony from two independent witnesses who had seen the wills signed and understood their effect was sufficient. It also held that the word “irrevocable” need not appear in the wills themselves; what matters is the parties' intention at the time of execution, assessed from the wording used and the surrounding evidence. On the facts, the wills' mutual revocation clauses, references to an agreement between the makers, and language reflecting a shared intention regarding the property were together sufficient to establish a binding mutual wills arrangement.

Practical Implications for Estate Planning

For clients making wills in tandem with a spouse or partner, it is worth turning attention to three questions before signing. First, whether the arrangement is genuinely intended to be mutual and irrevocable, or simply mirrored for convenience and subject to change. Second, whether that intention has been properly documented at the time of execution, through clear instructions, attendance notes, or express wording in the wills, so that the position does not depend on the later recollection of witnesses. Third, for anyone revisiting an earlier will made jointly with a former spouse or partner, whether that earlier arrangement could be characterised as mutual, since a new will that departs from it may not achieve the intended result.

Mutual wills remain a relatively narrow area of probate law, but as this case demonstrates, the consequences of getting it wrong, or of not recognising that it applies, can be significant and can surface many years after the original wills were made. Proper legal advice at the time of drafting remains the most reliable way to avoid disputes of this kind.

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