The Turnbull government waited 13 hours before revealing cabinet minister Fiona Nash was a British citizen, which could potentially mean her election to the Senate is invalid.
Attorney-General George Brandis appeared before a Senate committee on Friday and defended the time it took the government to give Senator Nash the nod to reveal her dual citizenship status.
He blamed it on the unavailability of the solicitor-general - who was busy in the High Court on Thursday - to provide the government with advice until after 5pm.
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Senator Fiona Nash reveals she is a British citizen
Senator Nash made her announcement to the upper house at 7.05pm, after advice from a British QC was received at 5.40am.
The solicitor-general's advice was considered by Prime Minister Malcolm Turnbull, deputy Liberal leader Julie Bishop and Senator Brandis at 6.15pm.
"There were no delays," he told the committee.
"Senator Nash was in the chamber, disclosing this fact within 50 minutes of the solicitor-general's advice."
Senator Brandis acknowledged Senator Nash had a "sufficient level of concern" about her citizenship on Monday night, and she raised this with him and the prime minister.
But he said the facts had to be established because both her parents - including her Scottish-born father - were dead, making in difficult.
Senator Brandis again defended the decision of Nationals senator Matt Canavan to stand down from cabinet while his case of possible Italian citizenship was decided by the High Court.
His situation was different because it was leaked to the media and there was incomplete information, he said.
"If the story hadn't leaked, if we had been able to establish all the facts and circumstances before making a public statement it may well be that the view would be taken that Senator Canavan need not stand aside."
The High Court will also consider similar cases involving Deputy Prime Minister Barnaby Joyce, former Greens senator Larissa Waters and Scott Ludlam and One Nation's Malcolm Roberts.
