Mutual wills in New Zealand can bind the surviving partner even after remarriage — but only if the agreement was properly formed and a constructive trust arises on the first death. Without that, a new spouse can inherit everything and the original beneficiaries get nothing. Here is what couples in New Zealand need to understand before signing up for this arrangement.
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What mutual wills actually are
Mutual wills are two separate wills made by two people — usually spouses or partners — under a binding agreement not to revoke them. The agreement is the critical element. Two wills that happen to mirror each other are not mutual wills in the legal sense; they become mutual wills only when the testators promise each other they will not alter or revoke without consent.
New Zealand courts adopt the approach developed in English equity. The leading English authority remains Healey v Browne [2002] 2 WTLR 849, in which the court held that on the death of the first testator, a constructive trust arises over the survivor's estate to the extent needed to give effect to the agreement. The survivor can deal with the assets during their lifetime, but cannot defeat the agreement by revocation or by making a fresh will that contradicts it. New Zealand courts follow the same constructive trust analysis.
The effect of remarriage
Marriage or civil union revokes a will automatically under section 18 of the Wills Act 2007. A person who remarries after their first partner's death therefore has no will — unless they make a new one. The question is whether the constructive trust imposed at the first death survives that revocation.
The answer in New Zealand is yes, subject to proof of the original agreement. The constructive trust attaches to the estate at the moment the first testator dies. Remarriage and a new will do not extinguish a trust that has already crystallised. The survivor holds the relevant assets on trust for the agreed beneficiaries — typically the children of the first relationship — regardless of what a second will says.
Proving the agreement is where most claims fall apart. Courts require clear and satisfactory evidence of an actual contract: oral evidence alone is rarely sufficient, and a solicitor's attendance note or a recital in the wills themselves carries far more weight. Where the agreement is not documented, the survivor's estate (and any second spouse) will argue strenuously that no binding arrangement ever existed.
Family Protection Act 1955 claims cut across mutual wills
Even a perfectly documented mutual will cannot shut out claims under the Family Protection Act 1955. That Act allows the court to order provision from a deceased's estate for eligible claimants — children, spouses, civil union partners, and in some cases grandchildren — who have not received adequate maintenance and support.
A second spouse who survives the mutual-will testator qualifies as a claimant under the Family Protection Act. So do children of the second marriage. Their claims are assessed against the net estate, and the constructive trust assets can sometimes be caught within that assessment depending on how the court values the estate. The result is that mutual wills do not guarantee the first family receives everything the couple intended; Family Protection Act claims can reduce what passes under the constructive trust.
The Family Protection Act grants the court broad discretion to order provision from the deceased's estate in favour of eligible claimants. That discretion is exercised by reference to the claimant's need, the size of the estate, moral duty, and other competing claims. Courts have consistently held that a surviving second spouse has a strong presumptive entitlement, particularly where the marriage was of any real duration.
The Property (Relationships) Act 1976 adds another layer. A second spouse or de facto partner of three years or more has relationship property rights that arise independently of the will or any trust. Those rights are statutory and cannot be contracted away by an agreement made in a prior relationship.
Why mirror wills are safer for blended families
Mirror wills — where each partner leaves everything to the other, then equally to their children — look identical to mutual wills on paper but carry no binding agreement. Each person remains free to revoke or change their will at any time without the other's consent.
For blended families, that flexibility is usually the point. A surviving parent can update their will after remarriage to reflect changed circumstances: a new partner, children born of the second relationship, a child who has become estranged, or assets acquired after the first death. Mirror wills impose no obligation and attract no constructive trust.
The trade-off is obvious: the first family has no legal protection. A surviving parent who remarries and then dies leaving everything to the second spouse leaves the children of the first relationship with only a Family Protection Act claim, which is discretionary and costly to pursue.
Couples with children from previous relationships should weigh this carefully. A testamentary trust — created inside a standard will — can ring-fence assets for the first family without triggering the complex enforceability problems of mutual wills. The testamentary trust takes effect at the first death and operates under the Trustee Act 1956 and the Trusts Act 2019. It does not depend on the survivor's co-operation after the first death, and it survives remarriage, new wills, and relationship property claims (though the quantum of trust assets may be affected by those claims).
How courts assess whether an agreement existed
New Zealand courts apply a three-stage analysis: (1) was there an agreement not to revoke, (2) did the first testator die without revoking, and (3) did the survivor accept a benefit under the will? If all three are satisfied, the constructive trust is imposed.
The first stage is almost always the battleground. Courts look for contemporaneous written evidence — a contract separate from the wills themselves, a recital in the wills, or solicitor's attendance notes recording the agreement. A surviving spouse who denies that any agreement was made places the burden squarely on the claimant to prove otherwise, often against a deceased's estate where memory and documents are scarce.
Accepting a benefit under the first will is strong evidence but not conclusive. Courts have found constructive trusts even where the survivor disclaimed or varied the gift, provided the other elements of the agreement were clearly established.
What to do before signing mutual wills
Any couple considering mutual wills should address three things before execution. First, record the agreement explicitly — either in a separate deed or in a recital within each will stating that the wills are made pursuant to a binding agreement not to revoke without the other's written consent. Second, take independent legal advice, because the agreement binds both parties and the consequences of the first death are irreversible. Third, think hard about whether mutual wills are actually the right structure, or whether a testamentary trust or family trust achieves the same result with fewer problems.
Couples can use a New Zealand last will and testament as the base document and instruct their solicitor to include the necessary recital and cross-references. Forms-legal.com provides the template; the binding agreement itself requires careful legal drafting and independent advice for each party.
The 2026 position
No legislative changes have altered the core mutual wills framework since the Wills Act 2007 and the Trusts Act 2019 settled the landscape. The constructive trust approach remains good law in New Zealand. The Trusts Act 2019 does, however, impose mandatory duties on trustees and improved disclosure obligations, which means a surviving partner holding assets on constructive trust has more formal duties than they might have expected when the mutual wills were executed. Beneficiaries can now demand information about trust assets more easily, which strengthens enforcement.
The Family Protection Act 1955 and the Property (Relationships) Act 1976 remain the most significant practical limitations. No amount of careful mutual will drafting eliminates those statutory entitlements — they operate by force of law, not by agreement of the parties.
For most New Zealand couples with children from prior relationships, a combination of a well-drafted will and a testamentary trust beats mutual wills on both certainty and flexibility. Mutual wills answer a narrow need: couples who genuinely want to lock in a distribution and are prepared to accept that the survivor will be legally constrained for the rest of their life. That is a serious commitment, and the law treats it as one.
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This article is general information, not legal advice — see our accuracy & editorial policy. Confirm the cited law is current before relying on it.