Polling conducted for think tank The Australia Institute showed Pauline Hanson had the largest primary vote in the NSW electorate of Farrer at 28.7 per cent, ahead of the May 9 by-election.
The survey of almost 1300 Farrer residents showed independent Michelle Milthorpe had the next-highest support at 23.3 per cent, followed by the Liberals on 19.1 per cent, Labor on nine per cent and the Nationals on 5.2 per cent.
The by-election was triggered by the resignation of former Liberal leader Sussan Ley, who quit her seat after 25 years floowing being rolled by Angus Taylor in a leadership spill in February.
The four-way contest is considered a crucial test of Mr Taylor's newfound leadership of the Liberals, with Farrer always being held by the coalition since the seat was established in the 1940s.
One Nation has pre-selected agricultural businessman David Farley to run in Farrer, with the by-election also being an indicator of whether the party's rise in the polls translates to extra seats in parliament.
Ms Milthorpe is running for Farrer again after coming second at the 2025 election, narrowing the Liberals' margin in the former safe seat to 6.2 per cent.
Australia Institute chief executive Richard Denniss said the by-election would pose challenges for parties on multiple fronts.
"The Farrer by-election is shaping up as not just a big test for the Liberals, but for One Nation and the regional independent movement as well," he said.
"While Farrer is literally the Liberals' to lose, if One Nation can't convert strong polling into parliamentary seats, then it will be much harder for them to maintain momentum and voters' interests."
Despite Labor having almost 10 per cent support in the seat, the party is still yet to decide whether it will run a candidate.
The polling found if Labor did not stand in the Farrer by-election, 40 per cent of their supporters would give their vote to Ms Milthorpe, followed by 11.5 per cent to the Liberals.
Among the more then eight per cent of people who were undecided, 28.5 per cent leant towards the independent, followed by 26.1 per cent for One Nation and 18.2 per cent for the Liberals.
When asked who voters wanted to win the least, One Nation had the largest portion of 37.1 per cent.
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