Sometimes a person is released on bail on his or her own undertaking(that is, the person signs the agreement and personally guarantee to appear and comply with the conditions of the bail agreement). At other times a guarantor is required [Bail Act 1985 s.7].

A guarantor enters into a separate agreement known as a guarantee of bail, in which he/she guarantees that the person who is released on bail will comply with the bail agreement or with specified conditions of the bail agreement, and may be required to forfeit a sum of money if the person on bail fails to comply with a term or condition of the bail agreement. If a guarantor knows or reasonably suspects the person has breached a term or condition of the bail agreement the guarantor must take reasonable steps to notify the police or otherwise faces a fine of up to $1000 [Bail Act 1985 s.17a] in addition to forfeiting a sum of money.

A guarantee of bail is a serious, binding obligation and a guarantor will only be released from an obligation in extreme circumstances. A guarantor can apply to the court, which has the matter before it, to vary the conditions of the guarantee of bail or to revoke it at any time.