Quitting Victorian Liberal Ryan Smith has triggered a by-election test for the fractured state party as would-be replacements circle.

The former Baillieu/Napthine government minister has been the member for Warrandyte in Melbourne’s northeast for 16 years and his last day will be July 7.

“I have become increasingly uncomfortable with the growing negative tone of politics, both internally and more broadly,” Mr Smith said in a statement on Wednesday.

Victorian Liberal leader John Pesutto learned of Mr Smith’s resignation when he read his statement, which did not mention the party’s leadership team in a long list of thanks.

He refrained from criticising Mr Smith for exiting politics about six months after being re-elected for another four-year term, sparking the first state by-election since 2017.

“These things happen. People contest elections in the hope and expectation that we would win,” Mr Pesutto told reporters.

Mr Smith put his hand up to become party leader after the coalition’s election thumping last year before swinging his support behind Berwick MP Brad Battin, who lost to Mr Pesutto by a single vote.

He was then not included in Mr Pesutto’s shadow cabinet.

The Liberal Party has been beset by internal ruptures between conservative and more moderate members since the November state election.

Most recently it has been dealing with fallout of expelling first-term MP Moira Deeming after she attended an anti-transgender rights rally and threatened Mr Pesutto with defamation action.

At this month’s state conference in Bendigo, Mr Pesutto was booed and heckled by Ms Deeming’s supporters.

The saga prompted Opposition Leader Peter Dutton to flag the prospect of federal intervention in the Victorian branch if it could not resolve its issues.

The Warrandyte poll could be held any time between early August and late September, after the coalition’s historic by-election loss in the nearby federal seat of Aston in April.

Outgoing Liberal MP Ryan Smith’s statement of resignation.

Mr Pesutto plans to work closely with party administrators on a preselection pick to boost its chance of retaining the seat.

“We’re going to throw everything at it,” he said.

Mr Pesutto wants a woman to be considered for preselection, with 21 of the 30 Victorian Liberals’ MPs being men.

Federal Liberal vice president Caroline Inge is considering a run, along with former Kew MP Tim Smith after he didn’t recontest his inner-Melbourne seat following a drink-driving crash in 2021.

In November, Ryan Smith held Warrandyte on a 4.2 per cent two-party-preferred margin over Labor’s Naomi Oakley.

Ms Oakley, who also narrowly lost to Liberal Keith Wolahan at last year’s federal poll for the seat of Menzies, is waiting for Labor to decide whether it will contest the by-election before declaring her intentions.

The Liberals are struggling to attract electoral support in Victoria and the loss in Aston would make party officials nervous, Monash University political scientist Zareh Ghazarian said.

“If it loses, then the opposition leader will be in strife and the divisions within the party will continue to fester,” Dr Ghazarian said.

It will be the first Victorian state by-election to be held in more than five years, when Labor’s member for Northcote Fiona Richardson died after a battle with cancer.

The Liberals won a supplementary election for the regional Victorian seat of Narracan in January after the sudden death of Nationals candidate Shaun Gilchrist.

– AAP