A Liberal candidate's job at the Administrative Appeals Tribunal renders her incapable of being chosen as a senator to replace cabinet minister Fiona Nash, the High Court has been told.
The court will consider on Wednesday whether Hollie Hughes should be declared duly elected to replace Ms Nash as a NSW coalition senator.
Ms Nash was disqualified by the court after it found on October 27 she held dual citizenship, which went against section 44 of the constitution.
A special count by the Australian Electoral Commission resulted in a win for Ms Hughes, who was the next candidate after Ms Nash on the NSW coalition Senate ticket for the 2016 election.
However, Ms Hughes was working as a part-time member of the Administrative Appeals Tribunal until October 27 when the court determined there was a vacancy.
Amicus curiae Geoffrey Kennett SC, in a written submission, argued the AAT job was an "office of profit under the crown" - a reason for disqualification set out in the constitution.
It was "inconceivable", he wrote, that an AAT member could fulfil their duties simultaneously with that of a member of parliament.
Ms Hughes was incapable of being chosen because she held the AAT position between September 4-5, when the Senate resolved to refer the Nash case to the court, and October 27, he wrote.
Solicitor-General Stephen Donaghue accepted, in the government's submission, the AAT position was an office of profit under the crown.
However, he argued Ms Hughes should be duly elected because the process of "being chosen" started with nomination and concluded at the end of polling day.
The special count of ballots which resulted in Ms Hughes' election was "not a re-choosing but simply the proper identification of the electorate's choice made on polling day".
As well, Ms Hughes was appointed to the AAT from July 1 this year, nearly 12 months after polling day.
Ms Hughes' barrister Arthur Moses SC argued in his submission the votes which led to her taking the Senate seat were cast at the time of the 2016 election, when she was qualified to be in parliament.
"Whilst the period between nomination and the occurrence of a special count to fill a vacancy is part of the electoral process, once the votes are cast the choice has been made."