Liberal candidate Simon Kennedy has been elected successor to former prime minister Scott Morrison in the seat of Cook in Sydney's south.
Saturday's by-election was triggered after Mr Morrison announced his resignation from politics in January.
In a message on X on Saturday evening ABC election analyst Antony Green called the seat for the Liberals.
Six candidates had vied for the top spot including members of the Greens, the Animal Justice Party, the Libertarians, Sustainable Australia, and an independent.
Labor did not contest the seat.
Mr Kennedy was widely expected to take the safe Liberal seat, which has been in the party's hands since 1975, with a comfortable margin.
For his party, this is a chance to shake off Mr Morrison's fraught reputation and turn a new leaf, election analyst Kevin Bonham said.
"These days defeated prime ministers don't tend to hang around and it's been a nuisance having him there for as long as he's been there," he said.
"It's good for (the Liberals) to have him out of the way, have a new member in, and get on with things."
After his government lost power to Labor at the federal election in May 2022, Australia's 30th prime minister continued in politics as a backbencher.
But the fallout from his leadership would rattle parliament for months.
In August 2022, it was revealed he had appointed himself minister of health, home affairs, treasury, industry and finance at various times during the COVID-19 pandemic.
On Thursday, the controversial $550 million upgrade to the Australian War Memorial was revealed to have been approved by his government before a business case could be considered.
Although there was a protest vote against the Liberals and Mr Morrison at the 2022 election, it is unclear whether this will be replicated in the by-election as Labor has not put up a candidate in the seat.
"The margins in these by-elections that are not contested by both major parties are meaningless," Mr Bonham said.
Without a Labor candidate, voter turnout is also expected to drop, which has raised concerns at the Australian Electoral Commission.
Early voting numbers were down 11.2 per cent compared with the 2022 federal election and 13 per cent compared with the Indigenous voice referendum, according to AEC data released on Thursday.
Postal vote applications, which closed on Wednesday, were also down slightly.
