James Ashby told AAP the short four-week campaign did not give One Nation enough time to give a candidate a chance in the northern Brisbane electorate of Stafford.
The party polled just over 3 per cent in the seat in the 2024 state election.
"I don't want to burn candidates," he said.
"Why would you put a huge amount of resources and effort into a four-week campaign? I want our candidates to have a year."
Voters in the seat were forced to the polls after the sudden death of former independent MP Jimmy Sullivan in April.
Mr Sullivan - who had a 6.83 per cent swing against him in 2024 - was expelled from the Labor Party last May over legal and medical concerns.
The seat has been held by Labor for most of its history, with Mr Sullivan's father Terry serving as the member from 2001 to 2006.
But a political expert said that could change, in a result that would have ramifications for David Crisafulli's ruling LNP government, the Labor opposition and federal politics.
Griffith University political scientist Paul Williams said on Friday Fiona Hammond was likely to snatch the seat for the LNP with a predicted vote of 51-52 per cent after preferences are allocated.
Prof Williams also said One Nation had erred by failing to stand a candidate in the urban seat, where the party has historically struggled for traction.
"They wouldn't win it but six months ago it would have been impossible and now it's moved from impossible to unlikely," he said.
He said One Nation might have polled between 12 and 20 per cent or even more, almost guaranteeing an LNP victory on preferences.
But Ashby said One Nation had no interest in boosting the LNP's fortunes in the city.
"We're not here to prop the LNP up, just like they're not here to prop us up," he said.
"We've chosen to wait so our candidate can have a longer runway for the election, so they can do better than 15 per cent, better than 20 per cent.
"We're here to win seats and if that means off Labor or the LNP, we'll do it."
Labor, whose candidate Luke Richmond cast his vote with wife Maddie early on Saturday, notionally holds the seat with a 5.3 per cent two-party preferred margin.
Recent polling shows the LNP on track for an unexpected and historic victory.
With by-election swings towards a sitting government rare, Prof Williams said even a reduction in Labor's margin would technically be a loss for Labor and former premier Steven Miles.
Mr Miles said on Friday the by-election was an opportunity for voters in the seat to send the Crisafulli government a message.
He said the outcome of the election would not change either the government or the leadership of the Labor Party.
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