Independent South Australian senator Cory Bernardi has officially resigned from Federal Parliament after a career of 13 years, handing over his seat to the Liberal Party.

Key points: Cory Bernardi announced late last year he would end his 13-year political career

Cory Bernardi announced late last year he would end his 13-year political career His resignation letter was today received by the Senate president Scott Ryan

His resignation letter was today received by the Senate president Scott Ryan His seat will go to a Liberal candidate, as he was one when he was elected in 2016

Senate president Scott Ryan said he had received Mr Bernardi's letter of resignation on Monday, which would take effect immediately.

"I have received a letter of resignation from Cory Bernardi as a senator for South Australia. The resignation takes effect immediately," he said in a post on social media.

"I will shortly be writing to His Excellency the Hon Hieu Van Le, Governor of SA, to inform him of this vacancy, which will be filled in accordance with Section 15 of the Constitution."

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Mr Bernardi announced late last year he would be leaving politics at the end of 2019, with his "integrity intact and very few regrets".

"The timing is right, I just don't want to go back to it next year — I feel in a very happy and comfortable place," Senator Bernardi said on Sky News in November.

"If nothing else I opened up lots of conversations, I remained true to my values and principles. People will make judgments about whether they were right or wrong.

"One of the great things is my integrity is intact.

"I feel very comfortable with who I am and what I have spoken about and if I have regrets, there are very few."

Liberal candidates to vie for Senate seat

Mr Bernardi has often been touted as an outspoken critic of both same-sex marriage and climate change.

He quit the Liberal Party in 2017 to form the Australian Conservatives, but his party struggled to attract support at last year's federal election.

He announced in June last year that a "lack of political success" and money had meant he was deregistering the Australian Conservatives.

He secured a six-year Senate term when he was elected in 2016 and his resignation will now trigger a casual vacancy.

Despite him breaking away from the Liberals, the party will still have claim to the seat, as he was a Liberal member when elected.

Among the candidates tipped to contest his Senate seat will be former Law Council president Morry Bailes and SA Legislative Council president Andrew McLachlan.