High-profile former Gold Coast City councillor Cameron Caldwell won the federal seat for the LNP on Saturday against a field of 12 candidates including Labor's Letitia Del Fabbro.
"We are on the right path as a party," Mr Caldwell said.
"We have a great leader and we will return to government."
The swing to the LNP on a two-party preferred basis was 2.4 per cent, making it an even safer coalition seat, according to Australian Electoral Commission data.
Mr Marles said the win was a "lethargic" result for Opposition Leader Peter Dutton.
"We really have been focused on the cost of living since the moment that we came to government," he told Sky News on Sunday.
"The idea that Peter Dutton as a Queenslander, who is leading the Liberal Party, would take any comfort out of this result at all, frankly, is ridiculous."
Mr Marles denied Labor had a problem with Queensland voters, describing the state as a place of "significant opportunity".
But Deputy Liberal Leader Sussan Ley dismissed the government's comments on their loss.
"It is a strong result," she said.
"I've listened to the Labor Party turn this into politics ... when they as the government should be enacting policies and caring a lot more for the people they've left behind.
"I was on the ground at many polling booths and you get that sense of cost of living crunch anxiety about the future."
Ms Ley denied there had been questions surrounding Mr Dutton's leadership of the coalition.
Treasurer Jim Chalmers said the LNP underperformed against the historical average, with a typical four per cent swing against the government in by-elections.
Mr Caldwell will replace former Turnbull and Morrison government minister Stuart Robert, who resigned from federal parliament in April this year.
The incoming MP fought off a tough campaign by Labor, which had highlighted Mr Robert's involvement in the robodebt scandal that engulfed the previous coalition federal government.
Robodebt is the unlawful debt recovery program that saddled almost 500,000 welfare recipients with hundreds of millions of dollars in false Centrelink debts between 2015 and 2019.
But Mr Caldwell said the main issue for voters in the Fadden by-election was the rising cost of living.
"We are a party that must return to government in order to restore the faith that Australians have in government keeping their promises," he said in his victory speech alongside his wife Lauren on Saturday night.
Mr Dutton said Mr Caldwell would be an exceptional member of parliament.
"He's worked tirelessly for this community for over a dozen years, he's accomplished in law in small business, he's worked hard for his local community, and he will continue that work as the federal member for Fadden," he said.
In her concession speech, Ms Del Fabbro said it was still a "bloody good result" for Labor.
"As you know, we knew this would be an uphill battle, so I guess it has always been an important message to the LNP to not take the Gold Coast for granted," she said in her concession speech.
Labor has won Fadden only once, in 1983 at the election of the Hawke government.
