The 37-year-old emphatically won a leadership ballot on Monday after former leader David Speirs stepped down on Thursday and he was quick to remind media of his surprise win over Mr Xenophon, who had quit the senate to try to return to state politics.
"I know that there's many of you that thought that I wouldn't win around seven years ago, but what I'm here to tell (Premier) Peter Malinauskas ... and everyone else, is no one thought I would win back then, and I won," Mr Tarzia said.
Nick Xenophon was beaten in the state election by Vincent Tarzia. (Tracey Nearmy/AAP PHOTOS)
Mr Xenophon was known as the "stunt man" of Australian politics, first in the SA upper house on a "no pokies" platform and then as a senator for South Australia from 2008 to 2017.
But his bid to dislodge Mr Tarzia from the inner-eastern suburban seat of Hartley failed, despite an early lead in opinion polls, and the victory earned Mr Tarzia a promotion as the youngest Speaker in SA history.
Mr Tarzia's colleagues hope he can lead the party out of the wilderness after its 2022 wipeout as a one-term government.
He defeated Josh Teague 18-4 in the leadership ballot.
At his first media conference as leader, Mr Tarzia confidently declared "the Liberal Party will win the state election in 2026".
Mr Tarzia said he could "categorically rule out" having undermined Mr Speirs, who quit after weeks of speculation about his leadership, saying he had "had a gutful".
David Speirs stepped down after serving as opposition leader since April 2022. (Abe Maddison/AAP PHOTOS)
"I absolutely did not undermine David and I consider David a friend. In the Liberal Party, we need David," he said.
Mr Speirs on Friday had said he would find it difficult to remain in the party if unnamed colleagues "were rewarded".
Mr Tarzia entered the SA parliament in 2014 when he won Hartley from Labor.
He completed law and commerce degrees at the University of Adelaide and was a solicitor before being elected as a councillor at the City of Norwood, Payneham and St Peters in 2010.
The former Speaker, who later became a minister in Steven Marshall's one-term government, said he was "willing to fight day and night" to hold the Labor government to account and to put forward an alternative policy platform to earn the trust of South Australians.
Vincent Tarzia served as a minister in the Marshall government. (Tracey Nearmy/AAP PHOTOS)
He said his first act would be to offer an olive branch to the ambulance union over the state's ramping crisis, a key issue at the 2022 election when Labor claimed victory after vowing to fix the logjam of ambulances plaguing emergency departments.
John Gardner, who ruled himself out of the Liberal leadership vote, remains the party's deputy leader.
Flinders University political analysts Rob Manwaring and Josh Sunman said Mr Tarzia would need to achieve balance in a party besieged by factional problems and develop a clear and distinctive policy agenda.
"It remains far from clear what the Liberals stand for and what significant policy options they will present to voters as an alternative government," the analysts said in a statement.
