Pauline Hanson's party claimed the Secret Harbour by-election late on Saturday evening AEST, however Labor candidate Georgia Tree is yet to concede.
One Nation's Luke Herdegen held a 14.08 per cent lead over Ms Tree in the two candidate preferred vote, when WA Electoral Commission counting closed on Saturday with 74.54 per cent of the vote counted.
"There are no safe Labor seats in this state, or in this country any more," Mr Herdegen told a jubilant crowd.
Mr Herdegen secured 39.08 per cent of first preference results according to the electoral commission, ahead of Ms Tree's 24.43 per cent and Liberal candidate Ryan Robertson holding 17.29 per cent.
WA One Nation Leader Rod Caddies noted the historic moment as he declared "the two-party system is dead".
"You're witnessing a result they said was impossible," he said.
"Labor have owned this part of Perth. But a safe seat does not stay safe if you ignore it long enough.
"Tonight Labor found out the hard way."
Mr Herdegen has been buoyed by a sea of polling booth orange across the beachside electorate, south of Perth.
"The vibe has been really strong for the last six weeks," he told AAP earlier on Saturday.
"We're feeling confident but ... it's a big margin. The swing is definitely on but it's just a matter of how big."
One Nation's performance in WA will be of interest across the nation, particularly Victoria with a state election looming in November.
On the ground in Secret Harbour, Labor is on the nose, with cost-of-living pressures, housing and a perceived lack of community amenities topping lists of voter concerns.
Local Luke Pors voted for One Nation and believes it will do a better job than either Labor or Liberal.
"We know what their true goal is and I think just in One Nation we trust," he said.
The Qantas flight attendant was also impressed by Mr Herdegen's campaign.
"He's like a home buddy and as obviously a youngie; we can really connect with him," he said.
Retirees Ann and Les Scard also voted One Nation.
"It has been a pretty strong campaign by Luke Herdegen," Mr Scard said.
"He deserves a chance.
"I get the impression Liberal and Labor are desperate; they're doing everything to try and discredit them and I don't think they're being successful."
10°C