The unanimous full bench decision of the High Court, sitting as the Court of Disputed Returns, puts an end to the former One Nation senator's battle to stay in the upper house, regardless of the outcome of any of his other court battles, which include challenging a Federal Court bankruptcy ruling.

Mr Culleton was not in court for the judgment.

Parliament will not know who takes his place until after a recount. The Electoral Commission will now consider the ballots as if Mr Culleton's name had not existed on the ticket.

His brother-in-law, Peter Georgiou, who was the number two candidate for One Nation at the July 2 election, is considered most likely to fill the vacancy. Mr Culleton has previously vowed to return to Parliament House as his chief of staff.

Mr Culleton quit One Nation in early December, amid reports of a growing rift with party leader, Pauline Hanson. The rift emerged after Senator Hanson swung her party's support behind a government motion referring Mr Culleton's election to the High Court.

The High Court judges found that Mr Culleton was not eligible to stand for the Senate at the time of his election, because he had been convicted and was subject to be sentenced for an offence that carried a year or more imprisonment.

That related to a larceny charge from New South Wales over a 2014 dispute with a tow truck driverwho arrived to repossess property from Mr Culleton's property, resulting in the loss of what Mr Culleton referred to as "a $7.50 key".

Mr Culleton was convicted in his absence by the Armidale Local Court in March 2016, but in August, following the election, won his bid to have the conviction annulled.

The Senate referred his election to the High Court given that, at the time he was elected, he was potentially ineligible under the constitution.

Mr Culleton's legal team argued that, given the conviction was annulled, it had never existed and therefore did not affect his eligibility.

But the court found that, at the time of the July 2016 election, Mr Culleton had been convicted and was subject to a term of imprisonment of more than a year "both as a matter of fact, and as a matter of law" and the later annulment "had no effect on that state of affairs".

A Federal Court ruling into Mr Culleton's bankruptcy is due to be handed down late on Friday, but will have no impact on his place in the Senate, as the High Court ruling is final.

He accused the party of "un-Australian behaviour" and having betrayed their election promises.

Senator Hanson described her former senator as a "pain in my backside" and said she was happy to see him leave the party.

The court ordered the Commonwealth to pay Mr Culleton's legal costs.

While the Senate vacancy still remains subject to a recount, One Nation's showing in the July election has given Senator Hanson confidence to welcome Mr Georgiou "to the team", releasing a statement 
calling him "an asset" for the Senate and someone who "will serve the people of Western Australia with distinction and dedication", while taking one last swipe at Mr Culleton.

"After meeting Peter and getting to know him, it is clear he is a dedicated, hardworking man who believes strongly in the principles of One Nation," she said.

"...Peter's not a career politician, he has real world experience and real world insight that will be invaluable to the party and the to the people of Australia on the floor of the Senate.

"...One Nation is united in our excitement at the prospect of working with Peter Georgiou and, honestly, I couldn't be happier.  It looks like One Nation and Western Australia will be getting a significant senator upgrade."

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