Ex-Liberal senator Cory Bernardi resigns

Paul Osborne
Independent senator Cory Bernardi has formally resigned from parliament

Independent senator Cory Bernardi has formally resigned from parliament, setting in train a three-way Liberal preselection battle in South Australia.

Mr Bernardi was elected as a Liberal, so his former party will fill his casual vacancy and not the Australian Conservatives party he formed in 2017, which disbanded in June 2019.

Senate President Scott Ryan said on Monday he had received the letter of resignation, which was effective immediately, and would be informing the SA governor of the vacancy.

The SA Liberals will hold a preselection ballot in Adelaide on February 1 involving around 300 members.

The three candidates are former Law Council president Morry Bailes, SA Legislative Council president Andrew McLachlan and business consultant Michael Van Dissel.

The winning candidate won't be able to take their Senate seat until the SA parliament endorses him, which could occur as early as February 5.

Once the position is filled, the government's Senate numbers will be lifted to 36 in the 76-seat chamber.