It was not enough for Gallagher to merely have taken steps to renounce her foreign citizenship, or foreign laws simply posing an obstacle. The High Court subsequently cleared him to stay in federal parliament, should he have chosen to do so.
Ms Gallagher said she was very disappointed by the outcome but she respected the decision of the Court.
Following Labor Senator Katy Gallagher's disqualification from Parliament, four MPs with the same predicament have resigned.
Under Section 44 of the Australian Constitution, members of parliament are unable to have citizenship in another country, and must prove that they took "all reasonable steps" to renounce their citizenship before being elected.
But the man who will likely replace her in the Senate, the ACT Director of Professions Australia, David Smith said he was ready to step up and be a strong representative for the ACT, not just as a seat warmer.
Three ALP MPs, Josh Wilson from Western Australia, Queensland's Susan Lamb and Tasmania's Justine Keay, announced they will resign and recontest their seats, along with former Nick Xenophon Team MP Rebekha Sharkie from Adelaide.
"They must resign today, Bill Shorten must require the resignation of those three Labor members today", he said.
"Based on the recent High Court judgement, I will now take urgent legal advice", she said.
Australia's citizenship crisis came to a head last July, when the High Court reaffirmed an obscure 1901 law barring dual nationals from standing for public office.
WA is also facing a federal byelection in Perth after sitting MP Tim Hammond quit for family reasons and a state byelection in Darling Range after its MP for the seat, Barry Urban, quit following a damning parliamentary report which found he lied to parliament.
Meanwhile it is set to be one election after another with the Victorian state election expected to take place before the end of 2018 and in NSW next March, while Prime Minister Malcolm Turnbull said yet again on Wednesday that he wanted to call a general election in the first half of 2019.