Labor has declared its historic by-election win a ringing endorsement of the Albanese government, while federal Liberal leader Peter Dutton has promised to rebuild following the shock result for his party.
The ABC's Antony Green called the election for the ALP's Mary Doyle over the Liberals' Roshena Campbell, with the win the first time in a century that a government has won a seat from the opposition in a by-election.
Labor was predicted to take Aston with a swing of more than six per cent, holding 53 per cent of the two-candidate preferred vote to the Liberals' 47 per cent.
Late on Saturday, Labor had secured 41 per cent of the primary vote to the Liberals' 38 per cent and the Greens' 11 per cent.
In her victory speech, Ms Doyle said that even the most "optimistic true believers" had her pitted as the underdog in Aston, which had been in Liberal hands for more than 30 years.
"We were the underdog but boy, have we shown that we have a big bite," she told the party faithful.
"Even after the excellent result we had at the election last year, what we were trying to do hadn't been done for 100 years."
At the Liberals' event, Ms Campbell acknowledged that "tonight was not our night", but vowed that "for me, and our party - the Liberal Party - there is only one thing to do: we will fight on".
Mr Dutton told supporters that while it was a tough night for the party in Victoria, the Liberals would come together and rebuild.
The federal opposition leader said the Liberals had a lot of work ahead and must listen to the message sent by the voters of Aston.
Deputy Prime Minister Richard Marles hailed the election result as a "huge endorsement" of Prime Minister Anthony Albanese and Labor's focus on "bread and butter" issues.
Mr Marles said voters had responded to Mr Albanese's "serious and sincere" leadership and a government that was working to ease cost of living pressures.
An early swing towards Labor foreshadowed the Liberals' demise in the mortgage-belt electorate, where both Ms Doyle and Ms Campbell campaigned on cost of living pressures.
The result is a huge hit to the Liberals in a vote that was widely viewed as a test of Mr Dutton's leadership.
As the outcome became clear, federal Liberal MP Keith Wolahan issued a plea to his party to come together.
He also stood by Mr Dutton's leadership, adding: "I saw good and bad leaders in the most trying of circumstances and he has all the qualities of a good leader."
His comments were backed by fellow Victorian and senator Jane Hume, who said she "cannot imagine there would be any mood in the party room for (a change of leader)".
"There is no doubt this is a blow but he is a leader with a solid team behind him," she told the ABC.
Labor's Ms Doyle is a breast cancer survivor and former unionist who failed to take the seat at the last election.
Aston was held by the Liberals on a 2.8 per cent margin after former minister and outgoing member Alan Tudge suffered a large swing against him in 2022 election.
Other candidates for the seat were Angelica Di Camillo (Greens), Owen Miller (Fusion) and Maya Tesa (independent).
