Updated 4 November 2026
CM Law's Ultimate 50 List: Making a Will #38
In NSW, “revocable” and “irrevocable” wills are not two ordinary categories to choose between. A will remains revocable, but a binding agreement about what it must provide can create enforceable obligations. Understanding that distinction matters when couples want to support the survivor while preserving an inheritance for children or other beneficiaries.
Can you make a will that is legally irrevocable?
A will cannot be made irrevocable simply by describing it that way. A person with the required capacity can ordinarily make a later will or revoke an earlier one using a legally recognised method. However, a binding promise about their estate may still have consequences despite a valid change to the will.
The distinction between a will and contractual obligations is explained in Justice Lindsay’s paper on the nature of wills. A contract not to revoke a will, including a mutual wills arrangement, needs its own analysis. Revoking the testamentary document does not necessarily release the promise or remove the rights of people entitled to enforce it.
How do mirror wills differ from mutual wills?
Mirror wills contain matching or reciprocal provisions, commonly leaving assets to each other and then to the same beneficiaries. Mutual wills involve an additional binding agreement about the agreed estate plan. Making similar wills together does not, by itself, prove that either person promised never to change the arrangements.
The Australian Law Reform Commission’s discussion of mutual wills explains why proof of the agreement matters. Tell your lawyer whether you want flexibility or an enforceable commitment. A shared intention to look after children is not the same as a clearly established contract. Record the agreed obligations carefully, including when restrictions begin and what changes remain permitted.
How can you validly change or revoke a will?
The usual practical options are a new will or a properly executed codicil, which supplements an existing will. Section 11 of the Succession Act 2006 lists recognised revocation methods, while section 14 governs alterations. Obtain advice before marking, destroying or replacing the original, especially if a mutual wills agreement exists.
Under section 6, a formal will is ordinarily written and signed by the will-maker, or someone signing in their presence and at their direction. The will-maker signs or acknowledges the signature before at least two witnesses present together; at least two witnesses then sign in the will-maker’s presence.
Use witnesses who are not beneficiaries. Section 10 can invalidate a gift to an attesting beneficiary, subject to exceptions; it does not automatically invalidate the entire will. Section 8 allows the court to dispense with formal requirements in qualifying cases, but relying on that possibility can create uncertainty and expense. Destroying a newer will does not automatically revive an earlier one.
What happens after the first person dies under a mutual wills arrangement?
Where a binding mutual wills agreement applies and one person dies having performed their part, the survivor may remain bound to the agreed outcome. A later will can still be valid, while equity imposes obligations concerning the affected property. The agreement and surrounding circumstances determine the scope of those obligations.
A constructive trust is a remedy imposed by law to enforce the relevant obligation, rather than necessarily a trust expressly written into the will. The survivor may retain freedom to use property during life, depending on the bargain. Gifts or arrangements designed to defeat it can create problems. Beneficiaries should obtain advice before assuming either immediate ownership or an unrestricted right to stop spending.
What does a real case show about changing mutual wills?
In Birmingham v Renfrew [1937] HCA 52, the High Court upheld obligations arising from an agreement about wills after the surviving husband changed his will. His later will remained valid, but it did not remove the equitable obligations affecting the property covered by the agreement.
The wife had inherited substantial property. The couple made wills under an arrangement by which she left her residuary estate to her husband and he promised that, if she died first, he would leave his property to specified members of her family and would not change that arrangement.
After her death, the husband accepted benefits under her will. He later changed his will to favour his own relatives, reducing or removing benefits for her relatives. The High Court dismissed the appeal against the decision enforcing the agreement. The intended beneficiaries could enforce the resulting constructive trust against his executors.
This was an appeal from Victoria and is an important Australian authority. It demonstrates that a valid later will can coexist with enforceable obligations. The result depended on proof of the agreement, rather than the mere similarity of the earlier wills.
What should a mutual wills agreement address?
The agreement should define the promised benefits, the property covered and the survivor’s permitted choices. Consider changes in housing, health, relationships and family needs. Greater certainty for intended beneficiaries may come with substantial restrictions for the survivor, so both people should understand the commitment and obtain advice before signing.
Discuss whether the arrangement covers only inherited property or also other assets, sale proceeds and later acquisitions. Address ordinary living costs, aged care, gifts, remarriage, replacement beneficiaries and any agreed release or variation process. Do not assume that notice alone cancels the contract. Ask whether separate legal advice is needed and compare alternatives such as a testamentary trust or a right of occupation.
Do mutual wills prevent challenges or protect assets from every claim?
Neither a will nor a mutual wills agreement makes an estate immune from disputes. Questions about capacity, coercion, execution and the agreement’s existence can still arise. Eligible people may also seek family provision. Labelling a document “irrevocable” does not create general protection from creditors or guarantee a particular inheritance.
A family provision claim in NSW usually must be filed within 12 months of death, unless the court permits a late application. It concerns adequate provision for an eligible person and differs from challenging a will’s validity. Under section 95 of the Succession Act, a release of family provision rights requires court approval. A private agreement alone cannot be assumed to exclude those rights.
Will every asset pass under the will?
A will primarily deals with property forming part of the deceased estate. Assets owned as joint tenants generally pass to the surviving owner, while superannuation and insurance may be paid outside the estate. An effective plan must coordinate ownership, nominations, trust arrangements and any mutual wills obligations, rather than relying on the will alone.
The NSW Government’s wills guide explains these distinctions. Check the property title and obtain current superannuation nomination information. For company or trust interests, identify what you personally own and which documents control succession. Obtain separate advice for overseas assets. The fact that an asset passes outside the will does not justify assuming it is beyond every possible legal claim.
How do capacity, marriage and divorce affect an existing will?
Review your will when relationships or decision-making capacity change. Marriage generally revokes a will, subject to statutory exceptions. Divorce generally removes specified gifts and appointments involving a former spouse, rather than cancelling the whole document. Separation alone does not automatically revoke it. Existing contractual obligations also need separate consideration.
Legal Aid NSW explains that an attorney or enduring guardian cannot rewrite your will for you. The Supreme Court has a separate power under section 18 to authorise a will, alteration or revocation for someone lacking testamentary capacity. If capacity or pressure from others is a concern, seek prompt advice about independent instructions and appropriate evidence rather than postponing the issue.
What should you bring to an estate planning appointment?
Bring existing wills, codicils and any agreement about inheritance, together with an asset and liability list. Identify children from all relationships, dependants, proposed executors and intended beneficiaries. Explain how much freedom the survivor should retain, and what benefits you want preserved. These instructions help determine whether mutual wills suit your circumstances.
Ask how the plan would operate if the survivor needs to sell the home, fund care or support a new dependant. Keep signed documents together and tell the executor where the originals are held. CM Lawyers can assist with wills and estate planning in NSW. Contact Christine Manolakos and the team on (02) 9557 9000 or lawyers@cmlaw.com.au.
This article provides general information about NSW wills and estate planning. It is not a substitute for legal advice about your circumstances, documents and obligations.
Key resources
Succession Act 2006 (NSW) — Execution, revocation, alteration, court-authorised wills and family provision.
Legal Aid NSW — Making a will — Updating wills, capacity, attorneys and relationship changes.
NSW Government — Learn about wills — Estate planning, ownership, non-estate assets and document storage.
ALRC — Mutual Wills: An Ancient Doctrine with Modern Teeth — Agreements, mirror wills and the survivor’s obligations.
Birmingham v Renfrew [1937] HCA 52; (1937) 57 CLR 666 — Official judgment. High Court case page. Relevant reasons appear at CLR pages 674–677, 682–683 and 689–690; the appeal outcome appears at page 694.
Supreme Court of NSW — What is a Will and Why Does It Matter — Justice Lindsay’s explanation of testamentary documents and contractual obligations.
Legal Aid NSW — Family provision claims — Eligibility, time limits and the court’s assessment.
Supreme Court of NSW — Contested proceedings — Will validity disputes and family provision proceedings.
