Australian voters face five by-elections across the country after Labor M-Ps Justine Keay [[KAY]], Josh Wilson, Susan Lamb and Independent Rebekha [[re-BEK-uh]] Sharkie became the latest parliamentarians to resign over their dual citizenship status because of the similarities between their cases and Ms Gallagher's.
Ms Gallagher had argued she took all reasonable steps to renounce her citizenship before the closure of nominations for the 2016 poll, despite the Commonwealth claiming she didn't make those efforts early enough.
The United Kingdom Home Office didn't register her renunciation of British citizenship until August, more than a month after the election.
Despite the loss, Ms Gallagher says she'll recontest her seat at the resulting by-election.
I will keep fighting because Mr Speaker, I am not done. Speaker this is not a valedictory speech, let me be very clear. I’m putting the government on notice, that while ultimately this decision will lay in the hands of the amazing people of Longman, I intend to be back.
The resignations will force voters into by-elections across the country, and another one caused by the resignation of Labor M-P Tim Hammond, who resigned last week for family reasons.
Ms Gallagher became the 11th politician to be forced from federal parliament for holding dual citizenship at the time they were elected, breaching Section 44 of the Constitution.
The government says Labor leader Bill Shorten should have forced the three Labor M-Ps that were affected by the High Court ruling to resign.
The government itself could have referred them to the court, but attorney general Christian Porter says that would not have been appropriate.
"To refer would have been to very much politicise an issue that could have been dealt with by Bill Shorten showing a leadership position and asking these three (the Labor MPs) to resign. So we have, yes, taken a very procedural course, put this absolutely beyond doubt. Our view was always that there was little or no doubt with respect to this in or about of October last year."
London-born West Australian Labor M-P Josh Wilson claims the High Court's Gallagher decision overturns what Labor says was 25 years of accepted practise that it was enough to take "reasonable steps" to renounce citizenship.
He says a new precedent has been set that will deter Australian citizens from taking up federal politics.
We shouldn't underestimate the impact of the interpretation that's been provided today. It will change the way the electoral system works in this country. It will mean for up to one fifth of all Australian citizens who are, or who may be entitled to citizenship of another country, that their ability to participate in Federal Elections will be significantly constrained.]]
When the dual citizenship saga was engulfing mostly Liberals last year, Labor insisted its politicians were all in the clear.
National Secretary of the Australian Labor Party Noah Carroll said in a statement in August that Labor had "an extensive and exhaustive process for ensuring that every candidate satisfies all constitutional requirements before they are nominated, including Section 44" as well as including declaring their citizenship status of their parents and grandparents.
Labor leader Bill Shorten has justified his decision not to demand the resignation of the Labor M-Ps affected by the High Court ruling by insisting they took all reasonable steps to ensure they were within the law.
Mr Shorten says he acted in good faith and in line with legal advice Labor had received on the matter.
We relied on our legal advice which says all reasonable steps. Now what the High Court has said is that all reasonable steps has to include the bureaucratic processing systems of a foreign government. That hasn't been the advice we've received. Whether or not we like what the High Court has decided, they've made that decision and we're going to get on with it.
In total, including the resignations that followed the High Court ruling, 15 M-Ps have left the current parliament because of dual citizenship.
