How are casual vacancies in the Senate filled?

Section 15 of the Australian Constitution outlines how a casual vacancy in the Senate is filled. If a senator resigns or dies while in office, a replacement is chosen to fill the casual vacancy by the parliament of the state or territory which the vacating senator represented.

Under a change to the Constitution in 1977, the newly appointed senator must be a member of the same political party as the vacating senator.

If the vacating senator is an independent or was elected as a member of a party that no longer exists, the state or territory parliament with responsibility to fill the vacancy decides on an appropriate replacement.

If the senator was elected as a member of a political party but left that party to become an independent – or join a different party – the casual vacancy is filled by someone from the original party.

The new senator serves the rest of the vacating senator’s term in the Senate.