Basil Zempilas replaced Libby Mettam on Tuesday as the head of the party, saying he would work hard and listen to his colleagues and the community.
"This is a new-look Liberal Party of Western Australia," he told reporters on the steps of the state parliament in Perth.
"A reset is under way and the road to 2029 begins today."
The Perth media personality and former Lord Mayor of the city said he would lead "collaboratively, harmoniously and decisively in holding this government to account".
"Every decision we make, every item that we raise with the Cook Labor government of (WA) will be raised with the intention of making that government better," he said.
Mr Zempilas, who narrowly won the seat of Churchlands at the election on March 8, said the party "did not resonate the way we would have hoped at the previous election".
"The way to step forward, the way for the reset of the Liberal Party in Western Australia to really begin, to gather momentum ... is to be out in the community and listening," he said.
Latest counting in the state poll shows Labor won 46 of 59 seats, the Liberals seven and the Nationals six, after the Liberals claimed the final lower house seat of Kalamunda on Monday night.
"By winning Kalamunda, we have seven members of the lower house and that is more than three times what we had at the corresponding time of the (last) parliament," said Mr Zempilas, a former footballer, television and radio presenter and Seven Network sports commentator.
Mr Zempilas, who has no parliamentary experience and severed his ties with Seven West Media earlier in March, is also set to become the state's opposition leader.
The Nationals were the opposition after Labor's 53-seat landslide 2021 election victory left the Liberals with just two lower house seats to the Nationals' four.
Asked about his lack of experience, Mr Zempilas said: "It doesn't matter how you get here, it's what you do when you get here and what you bring with you".
He deflected questions about whether he would be the next WA premier.
"I'm not here today to talk about what I might do if I become premier ... that is not something that is in my mind right now," he said in a polished media performance.
Mr Zempilas, who is well-known nationally for his commentary call of Steven Bradbury's famous come-from-behind win at the 2002 Salt Lake City Winter Olympics in a speed skating event, said his first order of business was to establish how the Liberals and the Nationals, who previously had an uneasy alliance, would work together in the new parliament.
Ms Mettam has become deputy leader after she announced she would not seek re-election for the leadership.
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