West Australian One Nation senator Rod Culleton has launched a strident defence of his position in the Senate, after the Federal Government revealed plans to challenge the validity of his election in the High Court.

It is the second Senate position in doubt, after the Coalition confirmed it would ask the Senate to consider the validity of Family First senator Bob Day's election.

Last week, Senator Culleton avoided having a conviction recorded against him after pleading guilty to larceny in a New South Wales court.

He was originally convicted of the offence when he failed to attend court to answer a charge of stealing the keys from a tow truck driver in northern New South Wales in 2014.

That conviction was later annulled, but the conviction stood at the time of the July 2 federal election.

Attorney-General George Brandis said he wrote to Senate President Stephen Parry on October 29 to share legal advice regarding Senator Culleton's elected position.

"The opinion was sought by me on 13 October 2016 in view of issues raised in proceedings commenced in the High Court against Senator Culleton by Mr Bruce Bell," he said.

"It appears that the proceedings brought by Mr Bell are based on an allegation that, at the time of the last election, Senator Culleton had been convicted of an offence punishable by a sentence of imprisonment for one year or longer, and was therefore 'incapable of being chosen' as a Senator under section 44(ii) of the Constitution."

That section of the Constitution states that if a person "has been convicted and is under sentence, or subject to be sentenced, for any offence" that carries a punishment of one year or longer imprisonment, they cannot serve in Parliament.

Senator Culleton said he would fight the case all the way - despite concerns about the integrity of the nation's highest court.

"There's an old saying, if you grab a tiger by the tail, you better hang on — the thing is scratching, but I'm hanging on," he said.

"I'm not sure whether I'm going to participate in any High Court jurisdiction.

"If I do, I'll simply go down and sheer a sheep and take the belly fleece and stick it over my head, and I'll represent myself."

He said he had been "exonerated" of the alleged offence.

"Some days, dog shit sticks to your boot, and unfortunately I'm wiping it off but it still stinks," Senator Culleton said.

"I need to perhaps go over to that garden hose, or that puddle, and give it a good wash."

Last month outgoing Solicitor-General Justin Gleeson told a Senate Committee he had been asked to advise the Government on a matter concerning the makeup of the Senate.

The ABC understands that related to Senator Culleton's tenure in the Upper House.

In August, Mr Bell spoke with the ABC about a petition he had lodged with the High Court challenging Senator Culleton's eligibility.

"It's perfectly clear under Section 44, he nominated and on a sworn form, whether it was knowingly or otherwise ... you say 'you're eligible', he wasn't, because he was under pain of sentence for a crime that potentially exceeded 12 months jail," he said.

Senator Culleton has taken out a restraining order against Mr Bell.