Independent Senator Cory Bernardi said it was a safe bet he would retire within three years.
Senator Bernardi deregistered his Australian Conservatives party on June 28, meaning the ex-Liberal senator's South Australian seat would go back to the Liberals should he retire via a casual vacancy.
Mr Bernardi’s departure means the Coalition will increase its numbers in the Senate from 35 to 36, reducing its reliance on the crossbench.