* Mathias Cormann to retire as finance minister and government Senate leader and quit parliament on October 30. He will be nominated by Australia to be OECD secretary-general.

* Simon Birmingham to take on both roles at that time, adding them to his current role as trade minister.

* Michaelia Cash to be deputy government Senate leader, taking over from Senator Birmingham.

* Wider ministry reshuffle to occur after parliament rises for the year on December 10.