The South Australian, who has voted with the government on almost all legislation since his defection in February 2017, confirmed his decision to The Sydney Morning Herald and The Age on Tuesday night.

"I realise that my enthusiasm to return to parliament in the new year had gone and it's time to move on with other aspects of my life and let others pick up the cudgels," he said.

Senator Bernardi had hoped to steal One Nation votes in forming his breakaway party, but has failed at every election since to make any gains.

He took a parting shot at One Nation leader Pauline Hanson's tactics.

"In reflecting on my time in parliament I'm happy I always stuck to my principles and supported proven policy, rather than succumb to the siren call of the victimhood of populism," he said.

He is expected to give his valedictory on December 4, the last Parliamentary sitting week of the year.

Because Senator Bernardi was elected to the Senate as a Liberal his spot will be filled by the South Australian Liberals. Bernardi himself entered parliament in 2006 by filling the casual vacancy left by the former cabinet minister Robert Hill.

He fell out with the party when Malcolm Turnbull, his factional foe, was reinstalled as party leader and prime minister in 2015.

Senator Bernardi and some of Mr Turnbull's backers in 2015 were the driving force behind the then member for Wentworth's ousting as party leader in opposition in 2009.

He deregistered the Australian Conservatives party in June this year after a poor federal election result, which he believed was due to supporters endorsing Scott Morrison's elevation to the Liberal leadership.

Earlier this year he said that by June 2020 he would have turned 50 and served in the parliament for 14 years.

The coalition will have 36 senators when the vacancy is filled, requiring only three extra votes for a majority to pass legislation and motions.