"How are casual vacancies in the senate decided now?"

Section 15 of the Australian Constitution states that when a casual vacancy occurs in the Senate, through resignation, absence or death of a senator, a new appointment is made by the Parliament of the state which that senator represented, or, in the case of a territory, by their legislative assembly.

In 1977, the Constitution was altered by referendum to require that the vacant place be filled by a member of the same political party or group as the vacating senator. Prior to this change it had been a convention (usual practice), rather than a condition, that the replacement senator be from the same party or group.

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