A guardian has the power to make the range of personal or lifestyle decisions which the Board specifies in its order appointing the guardian.

A guardian can only be a natural person (not a corporation) over 18 years of age. There may be more than one guardian. A guardian may also be appointed as an administrator. Generally a guardian will be a family member or friend who is familiar with the person with a mental incapacity. Where there is no suitable relative or friend available the Board can appoint the Public Advocate as a guardian, see guardian of last resort. A person who cares for the person with a mental incapacity in a paid, professional capacity cannot be appointed as a guardian.

The Board is required to limit the powers of a guardian to the minimum necessary in the circumstances. In their decision making, guardians must observe the same principles of substituted judgement as are required of the Board and any administrator appointed by the Board, see principles of substituted judgement.

Where the guardian has authority to make medical or dental decisions, the guardian can consent to any necessary treatment, except for terminations of pregnancy and sterilisation under the Guardianship and Administration Act, and electro-convulsive therapy (ECT) under the Mental Health Act.

With the specific direction or authority of the Board, a guardian may arrange for the person with a mental incapacity to reside in specified accommodation or to receive necessary medical or dental treatment and day-to-day care. With the Board’s consent [s.32], the guardian or a member of the police can return a person with a mental incapacity to a place of treatment or care, and/or the Board can authorise a guardian to legally detain the person with a mental incapacity in a specific place for treatment or care. However, a guardian cannot authorise the placement of the person in a correctional institution or a psychiatric facility, (known as an Approved Treatment Centre under the Mental Health Act). For information on the detention of a person with a mental illness, see mental health.

A guardian must work co-operatively with any administrator appointed by the Board. The Board provides a copy of any orders made at a hearing, which dictate the powers and any conditions and terms, to all relevant persons. The Board will also set a review date for its order.