He has been called before the Court of Disputed Returns after it emerged he had been convicted of larceny, which would have made him ineligible to stand.
His lawyer, Peter King, has told the court Senator Culleton had not been sentenced at the time and was not subject to a term of imprisonment.
The court has reserved its decision until Friday.
Outside the court, Senator Culleton says Attorney-General George Brandis's submission did him no favours in its reflection on his character.
"He said it was a hardened case. You know, what's a hardened case for annulment? And we're talking a little pocket key that was lost. So, essentially, to the Australian people, if you stay at a hotel and forget to hand your key in, you can now come to the High Court and be held up for stealing the hotel -- or, motel."
