The brother-in-law of former One Nation senator Rod Culleton has officially been confirmed as his replacement.

Key points: Peter Georgiou becomes One Nation's fourth senator

Peter Georgiou becomes One Nation's fourth senator Rod Culleton failed in a last-ditched attempt to adjourn the hearing

Rod Culleton failed in a last-ditched attempt to adjourn the hearing Pauline Hanson previously said Mr Georgiou would be an asset to the party

Peter Georgiou will now be One Nation's fourth senator, after the High Court ruled Mr Culleton's election was invalid.

Mr Culleton was disqualified because he had a larceny conviction at the time of the election.

The Court of Disputed Returns in Brisbane confirmed Mr Georgiou — the next-placed party candidate on the ballot paper — as the replacement on Friday.

Mr Culleton failed in a last ditch attempt to stop the court from replacing him in the Senate.

Chief Justice Susan Kiefel said Mr Culleton had made an application on Thursday to adjourn the hearing.

"He listed 10 matters in an email to the senior registrar. None of them have any relevance to the matter before the court today," she said.

"No purpose would therefore be served in granting the application."

The decision increases One Nation's power in the Senate crossbench, taking its count back up to four senators after Mr Culleton quit the party last year.

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One Nation leader Pauline Hanson previously stated Mr Georgiou would be an asset to the party, describing him last month as a "dedicated, hardworking man".

Mr Culleton has rejected the decision, saying that the matter had to go back to the Senate.

He also criticised the court process, telling the ABC that "I will do whatever a valid court order tells me to do".

Mr Culleton also ruled out working with his brother-in-law, saying he wouldn't "waste his energy".

The Senate referred the validity of Mr Culleton's election late last year, claiming he had a conviction against his name at the time of the federal vote for stealing a set of keys.

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Under the constitution, that would disqualify him from sitting in Federal Parliament.

Mr Culleton had argued he was in the clear because the conviction was annulled after the July 2 election, but the Commonwealth maintained he was disqualified from running for office at all times during the election process.

In December, the Federal Court ruled he was an "undischarged bankrupt" in a case brought by former business partners — another ground for disqualification from the Senate.

Earlier this year, Senate president Stephen Parry followed that disqualification and declared Mr Culleton's seat was vacant.