Ben Carroll's first act as premier is the royal commission Jacinta Allan refused

Ben Carroll's first act as Victoria's 50th premier is to call a royal commission into the construction sector.

It is the inquiry Jacinta Allan refused for months.

Mr Carroll announced it in his first statement after being sworn in at Government House on Tuesday afternoon, hours after Ms Allan resigned rather than contest a spill she was expected to lose.

Alongside the royal commission he will establish a special prosecutor to run in parallel, and give IBAC follow-the-money powers this term.

“Not in 2027, now,” the statement said.

“In my Government, integrity will not be optional. Whether in business, politics or the union movement, there will be zero tolerance for those who misuse their positions.”

Ms Allan had been under pressure for months over corruption on Big Build projects.

She refused a royal commission after corruption-busting lawyer Geoffrey Watson estimated it had cost the state $15 billion.

Mr Carroll drew the line himself.

“Let me make one thing very clear: I am not Daniel Andrews; I am not Jacinta Allan,” he said in the statement.

“I will do things differently, because different times require a new approach.”

He said a delegation of colleagues approached him on Monday to tell him Ms Allan had lost the caucus, and asked him to stand.

He framed the election as a two-way risk, warning that polling has Victoria on track for what he called Australia's first Liberal-One Nation government — one he said would cut hospitals, schools, frontline services, cheaper childcare and free TAFE.

The statement also committed to police funding and powers, and to treating government spending as something Victorians are entitled to be concerned about.

He said he had spoken to the police commissioner on Tuesday.

Mr Carroll, from Labor's smaller right faction, was elected unopposed after a caucus meeting that ran almost two hours and was loud enough to be heard from outside the room.

Attorney-General and Planning Minister Sonya Kilkenny signalled she would nominate, then withdrew — which is what kept the leadership out of a rank-and-file ballot of at least 29 days, four months from the election.

Transport Infrastructure Minister Gabrielle Williams, briefly interim leader after the resignation, defeated Steve Dimopoulos for the deputy leadership.

“Ben Carroll has been unanimously endorsed by the state parliamentary Labor party and as our next premier of Victoria,” returning officer Juliana Addison said.

Redbridge pollster Tony Barry, a former Liberal strategist, had said earlier on Tuesday that a new leader fixes nothing without a policy overhaul.

“Otherwise he's going to be completely open to the attack of same horse, different jockey,” he said.

Mr Carroll answered that within hours.

He has held Niddrie since 2012 and was education minister under Ms Allan.

He grew up in Airport West and has said his first job was at the local Kmart.

The election is on November 28.