Independent Cathy McGowan is now nearly 1500 votes ahead in the battle for the seat of Indi after election officials added a missing 1000 votes to her tally.
Liberal frontbencher Sophie Mirabella had been gaining on Ms McGowan as postal votes were counted, but on Wednesday officials realised there had been a discrepancy between the number of people who voted in the Senate and House of Representatives.
They found a bundle of 1003 votes from a Wangaratta prepoll centre which had not been included in Ms McGowan's tally.
The Australian Electoral Commission (AEC) officially added the votes to Ms McGowan's total late on Wednesday, giving her a lead of 1449 votes.
Ms McGowan, who has run a grassroots campaign backed by more than 600 volunteers, was delighted.
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"Isn't it amazing," she told AAP.
"You wouldn't want it to be the other way, would you? It would be shocking."
An AEC spokesman said the error was discovered as part of a number of checks and balances during counting.
A spokesman for Ms Mirabella would not comment, instead directing calls to Liberal Party headquarters.
State director Damien Mantach said there was no doubt the votes had given Ms McGowan a clear advantage.
"Despite this turn of events, we're hopeful of making up ground with the thousands of votes that are still to be counted," he said in a statement.
Indi, which is in Victoria's northeast and includes the towns of Wodonga, Wangaratta and Benalla was considered a fairly safe Liberal seat before the election and has been held by conservative parties since 1931.
