The Constitution Act 1889 received Royal Assent on 15 August 1890 and came into operation when proclaimed on 21 October 1890. This Act effectively established self government in Western Australia and the Legislative Assembly was established as the elected chamber, or lower house, of the Western Australian parliament.

The six stated roles and functions of the Legislative Assembley are:

• forming a government;

• approving the finance for government operations;

• scrutinising the government's performance;

• legislating;

• providing a forum for matters of public concern; and

• representing the people of Western Australia.