A guarantee is a binding promise of one person (the guarantor), to be answerable for the debt or obligation of another (the debtor), if that other defaults. Guarantees become enforceable by the person to whom the guarantee has been given (the creditor) when debtors have defaulted on their obligations.

In this article, we consider the circumstances where a guarantee may be unenforceable. The information is general only and does not constitute legal advice. We recommend obtaining professional advice relevant to your situation.

Formal requirements

A guarantee is a contract and will not generally be enforceable unless all the formalities of contract formation have been satisfied. As such, like all other contracts, a contract of guarantee must be supported by consideration passing from the creditor to the guarantor, unless the contract takes the form of a deed.

Typically, a guarantee is given in consideration for the creditor agreeing to enter into some type of agreement with the debtor at the request of the guarantor. Accordingly, a guarantee should proceed the provision of credit otherwise a guarantor can argue that it received nothing in exchange for giving the guarantee and the document will not be binding.

In addition to the above:

  • in states where the Statute of Frauds continues to apply, guarantees are required to be in writing; and
  • if obligations of co-guarantors are joint and several, there is authority that a guarantee is not binding unless each guarantor named in the document executes it.

Enforcement of guarantees

Even if a guarantee has been created in a manner which the law of contract considers to be binding, other laws are available to guarantors to avoid the obligation the guarantor has agreed to take on in the guarantee. These laws, which are discussed below, are found in legislation as well as the common law.

Misleading or deceptive conduct

Like any other contract, a guarantee can be set aside on the grounds that a party has entered into it acting on the misleading and deceptive conduct of the creditor or debtor.


Creditors have a limited general duty of disclosure to a guarantor. Guarantees have been set aside on the basis of a failure by the creditor to disclose unusual information. Furthermore, if a guarantor asks a question of the creditor, the creditor must answer it truthfully. A creditor must also disclose the truth about any misapprehension or unfounded assumption a guarantor may be acting upon.

Duress or Undue Influence

If a guarantee is procured by duress or undue influence by the creditor or debtor, it may be voidable. To succeed, a guarantor would need to show that the provision of the guarantee was not an independent act of the guarantor, acting of its own free will and based on full information.

Married Women

In Australia, where a creditor relies upon the husband to procure his wife’s consent to act as guarantor and there is actual undue influence by the husband, the transaction may be set aside by the wife unless she has received competent and independent advice.

In the absence of undue influence, the Courts have found that it would be unconscionable for a creditor to enforce a guarantee against a wife if she fails to understand the significance and effect of the transaction.

Unconscionable dealing

This is the most utilised ground for seeking to set aside a guarantee. Where it can be established that a guarantor was under a special disability or disadvantage in dealing with a creditor and the creditor seeks to take advantage of this, a court may set aside the guarantee. Examples of circumstances involving unconscionability include poverty, sickness, age, drunkenness and/or illiteracy.

Statutory relief against unconscionable conduct is provided by the Australian Securities and Investments Commission Act 2001 (Cth), the Competition and Consumer Act (Cth), and the Corporations Act 2001 (Cth) and, in NSW, by the Contracts Review Act 1980 (NSW).

Non est factum

This defence focuses on the absence of any consent of the guarantor to the document signed. It is available to those who are unable to read due to blindness or illiteracy and to those who are unable to have any understanding of the significance of the transaction because of some other disability.


A contract of guarantee can be unenforceable because of illegality. Some examples include:

  • where the making of the guarantee is expressly or impliedly prohibited by statute; and
  • where the effect of the guarantee is contrary to public policy or infringes public policy.


If you are seeking to obtain a guarantee or become a guarantor, we recommend that you seek legal advice. If you or someone you know wants more information or needs help or advice, please contact us on 03 9607 8279 or email [email protected].