The prospect of a by-election in Chapman’s seat loomed large after she repeatedly refused to rule out quitting parliament when asked by InDaily this month if she intended to serve out her full four-year term.

She confirmed her resignation late yesterday – just hours after the party-room elected Speirs to front its new leadership team, with Chapman’s moderate colleague John Gardner as his deputy.

Chapman told InDaily she “made the decision over Easter”, which she spent visiting family in Sydney.

“I don’t have anything further to add,” she said.

“Steven [Marshall] and I have had our time, I’ve made a decision, so that’s where we’re at… he’s made a public statement to stay on.”

She did not comment on the timing of her announcement which, coupled with her absence from yesterday’s ballot, underlined ongoing suggestions of a rift with Speirs – which he has continued to deny.

“I haven’t spoken to David [but] I obviously advised him as the new leader [of my decision],” she said.

Chapman is awaiting the outcome of an Ombudsman’s inquiry, which is expected to report within weeks, examining her decision to axe a proposed timber port on her native Kangaroo Island.

The decision has already sparked a conflict of interest probe that saw her lose a historic vote of no confidence in the House of Assembly late last year, prompting her exit as Deputy Premier.

The by-election is not expected until the end of May at the earliest – after next month’s federal poll, and just two months on from the Liberals’ state election defeat.

Asked whether her departure could offer a potential parachute for Marshall’s former chief of staff James Stevens, in the event he loses his federal seat of Sturt – which occupies the same footprint as Bragg – Chapman said: “That’s a matter entirely for the party.”

Speirs was diplomatic about the decision, saying in a statement it was “sad news for South Australian politics and for the Liberal Party”.

“Vickie has been a stalwart of the parliament for more than two decades and someone who I am proud to have worked with and have looked up to since before I was even elected,” he said.

“She leaves behind an immense legacy as South Australia’s first female Deputy Premier and first female Attorney-General.

“I thank her for her service to South Australia and the Liberal Party and wish her all the best in retirement.”

But Manager of Government Business Tom Koutsantonis was quick to weigh in, saying: “David Speirs’ leadership is barely six hours old and we have already seen a breathtaking explosion in Liberal Party divisions.”

“The SA Liberal Party is so hopelessly divided they can’t even elect a new leader without an outbreak of recriminations,” he said.

Chapman’s exit has sparked outrage amongst some colleagues, with the timing taking the gloss off a rare display of party unity after the leadership ballot.

But others insist the party needs to move on from its former deputy leader, who has loomed large over its era in Opposition from 2002, serving as a frontbencher throughout and as deputy leader on and off for 12 years.

“We don’t need a disrupter within the group,” said one MP.

“The Labor Party will come out now and say it’s a sign that Speirs hasn’t got everyone on side, but all it actually talks about is Vickie.

“I’m sorry there’s going to be a by-election, and the cost that goes with it – that’s so disrespectful – but as far as the party moving forward, what a huge favour.”

After his election as Liberal deputy leader yesterday, Gardner had declared that he hoped Chapman “serves the four years she’s been elected for”, saying “she certainly has a contribution to make”.