Where there is no will (an 'intestate estate')
A domestic partner is entitled to inherit an intestate estate (see If there is no will - distribution of the estate). There is no requirement that a person be legally married to the deceased in order to inherit.
For the purposes of inheritance of an intestate estate a domestic partner may be entitled to an equal share with a lawful spouse. see if there is no will - distribution of the estate.
Where there is a will
A domestic partner may also claim under section 6 of the Inheritance (Family Provision) Act 1972 (SA) as a spouse of the deceased, if she or he believes the will makes inadequate provision for her or him see Contesting a will - Inadequate Provision.