How are casual vacancies in the Senate filled?
A senator being sworn-in

David Foote/DPS Auspic
Description
A new senator stands in the Senate. He holds a holy book and reads an oath of allegiance to the Crown while other senators watch. When senators are sworn-in they typically do so on holy book that is significant to their faith, however using a religious text is not mandatory.
Permission should be sought from DPS AUSPIC for third-party or commercial uses of this image. To contact DPS AUSPIC email: auspic@aph.gov.au or phone: 02 6277 3342.
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.