The Labor Party has claimed the Liberal stronghold seat of Bennelong in Sydney's north shore for only the second time in more than 70 years.
The seat, which was once held by former prime minister John Howard, will now go to Labor's Jerome Laxale after a significant swing.
Liberal candidate Simon Kennedy was unable to succeed popular MP John Alexander who opted not to contest the election, squandering the party's 6.9 per cent margin.
Labor now has 73 seats, three seats short of forming a majority government.
ABC chief election analyst Antony Green said the postal votes came through for Labor.
"The postal vote that were counted today broke even," he said.
"The Coalition needed to improve their vote on the postal vote but today they broke even."
Bennelong takes in all of Ryde Council and smaller areas from Hornsby and Parramatta councils in an area covering 60 square kilometres on the lower north shore.
Mr Laxale, who had been mayor for Ryde Council for five years, had been quietly confident of his chances.
He congratulated Anthony Albanese on Twitter after being elected as the country's 31st Prime Minister.
"From housing commission to the lodge, this is the incredible promise of Australia," he said.
"I hope to be part of a government that continues to protect that tradition."
In April, Mr Kennedy appeared in a video opposing COVID-19 vaccine mandates and saying there may be concerns about the safety of mRNA vaccines at an event organised by Australia's anti-lockdown movement.
He also suggested it was wrong for people to have lost their jobs for refusing to get vaccinated.
Mr Kennedy later clarified his comments, saying vaccine mandates were a "complex and emotive issue".
Bennelong has been held by the Liberal Party for all but one term since its creation in 1949.
It was held by the Labor Party from 2007 to 2010, after Maxine McKew defeated Mr Howard.
Mr Alexander won the seat of Bennelong from Labor in the 2010 election.
In November 2021, the former tennis player opted not to contest the election, deciding to retire from politics.
