Nationals win Vic by-election in landslide

The landslide result in Gippsland South by-election shows country voters want a country party representing them, newly-elected Nationals MP Danny O'Brien says.

Mr O'Brien will replace the former party leader Peter Ryan in the traditionally conservative seat in the state's east after claiming almost three-quarters of the votes on a two-party preferred basis.

The Upper House MP beat Liberal candidate Scott Rossetti and Greens candidate Andrea Millsom, who ran a campaign focused on the issue of coal seam gas exploration.

Mr O'Brien said he expected the Greens campaign to have a bigger impact, especially in the absence of a Labor candidate.

But it appeared CSG wasn't a vote changer, he said.

"In the end one in two people in Gippsland voted for us," Mr O'Brien said.

"It just shows that country people do want a country based party to look after their interests."

Mr O'Brien's election to the lower house seat leaves a vacancy in the Upper House Eastern Victoria Region.

The Nationals will select someone to replace Mr O'Brien who will likely be sworn in the same day as Mr O'Brien.

Mr O'Brien said he was overwhelmed and absolutely humbled by the result.

The by-election in the lower house seat was triggered by the retirement of former Nationals state leader Peter Ryan.

Mr Ryan retained his seat, though with a 7 per cent swing against him, when Victoria's former coalition government was swept from office in the November 2014 state poll.

Gippsland South has been conservative seat for much of the last 80 years, held by the Country or National Party.