Australia's far-right One Nation party won a key by-election on Saturday in a rural seat that had been held by traditional conservatives for more than half a century.

Preliminary results showed its candidate, David Farley, was on track to win 59.1%, defeating the incumbent center-right Liberal Party by a wide margin.

It marks the first time One Nation has won a lower house seat in the federal parliament.

Farley, a former agribusiness executive, was the clear favorite heading into the contest for Farrer, a large agricultural electorate some 550 ​kilometers (340 miles) south of Sydney.

"We're like a mason with a chisel and a hammer, and we're carving the letters into the Australian democracy," Farley told cheering supporters.

"One Nation is at the end of its beginning — we are going through the ceiling," he said, pledging to bring down the cost of living.

Farley (C) said the election win is the 'biggest achievement' of his career Image: Hilary Wardaugh/AFP

Why was a by-election held?

The seat was left…