The Court was adjudicating on a matter referred to it by the federal Senate late last year - sitting as the Court of Disputed Returns - concerning Mr Culleton’s eligibility for election due to being convicted at the time for larceny.

The High Court’s ruling also determined that Mr Culleton will be replaced following a recount of votes.

That is likely to see the person second on One Nation’s WA Senate ticket elected which is Mr Culleton's brother-in-law Peter Georgiou.

“Today the High Court unanimously held that Rodney Norman Culleton was a person who was convicted and subject to be sentenced for an offence punishable by imprisonment for one year or longer at the time of the 2016 federal election, and therefore was incapable of being chosen as a Senator under s 44(ii) of the Constitution,” the judgment said.

“The Court held that Mr Culleton was convicted and subject to be sentenced for an offence punishable by imprisonment for one year or longer at the date of the 2016 election, both as a matter of fact and as a matter of law.

“The subsequent annulment of the conviction had no effect on that state of affairs.

“The Court held that the resulting vacancy should be filled by a special count of the ballot papers.”