Independent Cathy McGowan is now nearly 1,500 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 1,003 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 1,449 votes.
Ms McGowan, who has run a grassroots campaign backed by more than 600 volunteers, was delighted.
"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.