"With considerable reluctance I consider that, because the system of election for the three Councils is proportional representation, it is necessary to declare all of the Councillors' elections void," Supreme Court judge Robert Beech-Jones said in his judgment on Thursday.
The election results for Kempsey, the City of Shellharbour and Singleton could have been different if all voters who registered to use iVote had been able to vote on the day, the NSW Electoral Commissioner argued in December.
The iVote system failed when registered voters were blocked from voting because the system failed to recognise their security credentials.
Voters will have to head to the polls once again for fresh elections.
Justice Beech-Jones noted that although the number of voters blocked iVote failure was small "the votes that were denied to those voters had the real potential to affect the election of at least one Councillor in each of the three subject elections".
The Electoral Commissioner approved last year's disputed results while waiting for the judgment, saying last year it would have been impossible to hold fresh elections until mid-2022, due to it being a federal election year.
In a statement on Wednesday, the commission said it would not use iVote at the state election scheduled for March 25, 2023 or at any by-elections between July 1 and then.
"The decision not to use iVote at the State general election in 2023 has not been driven by any concerns about cyber security matters in previous elections."
