Ben Carroll has called a royal commission into construction sector corruption and distanced himself from his unpopular predecessor on his first day as Victorian premier.
After being sworn in as the state's 50th premier on Tuesday afternoon, the 51-year-old sought to separate himself from the Labor leaders he had previously served.
"I am not Daniel Andrews, I am not Jacinta Allan," Mr Carroll told reporters.
"I will do things differently, because different times require a new approach."
Ms Allan had faced mounting pressure in recent months following revelations of corruption on Big Build projects.
She refused to call a royal commission into the sector after corruption-busting lawyer Geoffrey Watson estimated it had cost the state $15 billion.
In his first action as premier, Mr Carroll backflipped on Ms Allan's stance with a pledge to set up a royal commission.
Establishing the inquiry will be a priority and its terms of references will be "exhaustive", he said.
A previous commitment to give Victoria's anti-corruption watchdog "follow the money" powers in 2027 will also be fast-tracked to take effect before the November state election.
"Today we are saying 'enough is enough'. In my government, integrity will not be optional," Mr Carroll said.
"Whether in business, politics or the union movement, there will be zero tolerance for those that misuse their positions."
Mr Carroll, a former lawyer and political adviser from the party's smaller right faction, publicly ruled out challenging Ms Allan in June, looking the premier in the eye to declare he would not come for her job.
The Niddrie MP defended the about-face, saying "circumstances changed" after a cross-faction delegation told Ms Allan she had lost support of the majority of caucus.
Ms Allan, from the party's left faction, fell on her sword on Tuesday morning ahead of a caucus meeting where she was expected to lose a spill motion.
She initially flagged she would contest the leadership but reconsidered her position after speaking with colleagues overnight.
"I was prepared to put my record and my plan to a ballot of members, as our rules allow," Ms Allan said.
"I believe I would have won but doing so this close to an election takes up valuable resources, including the most precious one: time."
Shouting could be heard from inside the caucus room during the meeting that lasted almost two hours.
Attorney-General and Planning Minister Sonya Kilkenny signalled her intention to run for the leadership but dropped her nomination, avoiding a weeks-long election process involving votes of Labor MPs and rank-and-file members.
Senior minister Gabrielle Williams defeated Steve Dimopoulos, both from the left, in a ballot for the deputy leadership.
Ms Allan, who described herself as a team player, said she was proud to have served as Victoria's second female premier and would have relished leading Labor into the election.
She left the media conference without answering any questions, including whether she would remain in parliament after serving as the member for Bendigo East since 1999.
"Thank you and goodbye," Ms Allan said.
Prime Minister Anthony Albanese paid tribute to Ms Allan, calling her a "very decent human being" who could be proud of her achievements in politics.
"This will have been a very difficult day. Politics can be a very tough business," he said.
There was no guarantee Mr Carroll could lead Labor to a record fourth-straight election victory, Redbridge pollster and former Liberal strategist Tony Barry said.
A significant cabinet reshuffle and broader policy overhaul would be needed to differentiate Mr Carroll's politics from Ms Allan's and subsequently remedy the drop in voter support for Labor during her leadership, Mr Barry said.
"There's going to have to be changes around the Suburban Rail Loop and other things where he differentiates himself from Jacinta Allan," he said.
"Otherwise he's going to be completely open to the attack of same horse, different jockey."
"In that situation, he might make a bad situation even worse."
