The visit of Australia's future king, Prince William, reminds us of our failure to assert our full powers of self-government, writes UNSW Professor George Williams in the Sydney Morning Herald.

"The idea that someone should be born into the highest position in Australian Government is more than quaint; it is objectionable. It is inconsistent with what is otherwise a democratic and egalitarian system," writes Williams, who is UNSW's Anthony Mason Professor of law.

Selection by birth is not the only problem, he argues. Succession to the throne is determined by a 1701 English statute. It ranks men over women, and states that should Prince William convert to Catholicism or marry a Catholic, he will be 'for ever incapable to inherit, possess, or enjoy the Crown'.

"As the head of the Catholic Church in England has said, 'he can marry by law a Hindu, a Buddhist, anyone, but not a Roman Catholic'," Professor Williams writes.

It's time to assert our full powers of self-government by bringing about a sound and stable republican structure of government that better represents our aspirations and values, Professor Williams says.

To read the full opinion piece visit the SMH website.

George Williams is a member of the national committee of the Australian Republican Movement.