A visa holder can have his or her (usually his) visa cancelled if he fails the character test, under section 501 of the Migration Act. One way to fail that test is to be sentenced to imprisonment for 12 months or more. The term of imprisonment may be for a single offence, or it can the sum of more than one term.
If a person is held to have failed the test, his visa must be cancelled. It is mandatory. But the cancellation can be revoked, if a minister or her or his delegate (a public servant) decides to do so, or, in some cases, if the Administrative Appeals Commission decides that it should be revoked.