Alyssa Hayden, a two-term Barnett government upper house MP, beat Labor candidate Tania Lawrence, a former Woodside manager who was parachuted in after the government's first candidate Colleen Yates quit in a storm of controversy.

Ms Yates bowed out of the race days after being endorsed when it emerged she'd exaggerated her tertiary qualifications in an online profile.

It was a staggering development given the by-election was triggered by the resignation of Barry Urban after lies about his background - including wearing a police medal he wrongly claimed was for investigating war crimes in Bosnia - were uncovered.

Premier Mark McGowan blamed the loss on the two controversies, saying they had clearly hit Labor in the polling booths, although he didn't name names and added it was always hard to win a by-election in government.

"It was a very tough by-election and very tough circumstances as we are all aware," Mr McGowan told party members on Saturday.

The Liberal campaign also highlighted big hikes in household fees and charges, which kick in on July 1, labelling them broken election promises.

"The swing is a clear message to the Labor government: the community aren't happy with you and they're standing up for themselves," Opposition Leader Mike Nahan tweeted.

Labor still has a massive lower house majority of 40 out of 59 seats.

Australian Associated Press