Liberal candidate Ryan Robertson has flagged his run in the Secret Harbour by-election is unlikely to be his last in State politics if he loses, while remaining defiant his party can cause an upset.

As polling day began, One Nation and Labor were widely regarded as the two front-runners, with the Liberals running a distant third.

But Mr Robertson was refusing to concede defeat.

“For sure we can win, mate. I think it’s anyone’s game, absolutely,” he said.

“I don’t say that arrogantly, I say that, of course, with humility, but if anyone is going to lead West Australians with honesty and integrity, it’s the WA Liberal Party in my view.”

Mr Robertson, a Navy veteran and Rockingham councillor, joined the Liberal Party just 10 months ago.

While content with the effort he had put in, Mr Robertson did have one regret from the campaign.

“I feel really, really content that we have given it our all. Probably the only thing I would say on reflection would be that I probably should have spent more time with my wife,” he said.

“She’s done the hardest job out of all of this, and that’s been at home looking after our three daughters.

“To my beautiful wife, thank you for supporting me through this journey. My job has been the easy part in that respect.”

Regardless of the result, Mr Robertson indicated he would be back, saying the campaign had given him “a great love for politics”.

Liberal leader Basil Zempilas also backed his candidate, declaring he had a bright future in politics.

“If we are successful, that will be a great victory for us, but fighting a great campaign is also a great victory for us,” he said.

“We have found an outstanding candidate who I know has a very, very bright future in this space.

“If ultimately not successful tonight, I’m very confident that Ryan will put his hand up again.”

Mr Zempilas also stood by the Liberals’ campaign, saying he had “no regrets” about preferencing One Nation third or about his language, which prompted criticism from some within his own party that he had been too soft on the surging orange party.

“I have said consistently that the ultimate victory would be Ryan Robertson joining us in Parliament,” he said.

“But any result that means Labor do not hold a seat that they have always held ... will be a victory for all of those people who keep telling us they are frustrated by this Labor Government.”