In ruling against the federal government's stay request, Appeal Court Justice Robert Sharpe said Monday elections are rarely decided by a handful of votes as Ottawa argued they could be.
As such, Sharpe said, the prospect of causing "irreparable harm" by allowing those who want to cast a ballot to do so was "fairly remote."
Ottawa is appealing last month's court ruling that struck down a Canada Elections Act ban on voting rights for Canadians living abroad for more than five years. The feds argued on Friday for a stay pending disposition of that appeal.
However, Sharpe said it would be impossible to undo the potential harm to non-resident voters if they are stopped from voting in the June 30 byelections and the appeal goes in their favour.
"Once the election has passed, the constitutional right to vote in that election will be lost forever," Sharpe said.
Sharpe also rejected Ottawa's argument that some members of Parliament elected with the expats included in the vote would somehow be different from those previously elected.
"There is no air of reality to the claim that members of Parliament elected at byelection under a changed or amended law would be seen as different from their parliamentary colleagues elected under the earlier law," Sharpe wrote.
Sharpe noted that Elections Canada took immediate steps following the May 2 ruling to allow the non-resident citizens to vote.
A stay would force the agency to "undo what it has already done," something Sharpe said might not be practical.
He noted 13 people had registered to vote since the May 2 ruling and at least one had already voted.
"To grant a stay in this case would require Elections Canada to rescind the registrations of up to 13 non-resident electors and claw back the vote of a citizen who may well in the end have the right to cast her ballot," Sharpe said.
The justice also called it highly unlikely a flood of votes is likely from "disinterested and disengaged non-resident Canadians."
Last month, Ontario Superior Court Justice Michael Penny ruled in favour of two Canadians living in the U.S. They argued it was unconstitutional to deprive them of their right to vote simply because they had lived abroad for more than five years — a law that had been on the books since 1993 but was only recently enforced.