'Big Build' royal commission launched as poll nears

A royal commission into Victoria's scandal-plagued construction sector has been launched, with its leader and scope finalised.

Former South Australia chief justice Christopher Kourakis AC will steer the Royal Commission into the Integrity of Major Public and Civil Infrastructure Construction Projects in Victoria.

The announcement by Premier Ben Carroll comes 100 days out from the state election and follows a special cabinet meeting on Thursday morning.

"I chose someone independent, rigorous and fearless," Mr Carroll told reporters on Thursday afternoon.

Under the terms of reference, Mr Kourakis will probe the extent to which corruption, criminal conduct or serious misconduct has occurred on or in relation to any major public and civil infrastructure projects.

That includes any such activity undertaken or instigated by the CFMEU, construction companies and consortia, sub-contractors, labour-hire companies, contractors, suppliers or others.

The commission will be able to look into whether Victoria's executive government or delivery authorities adequately adhered to their roles and responsibilities in the oversight and governance of major construction projects.

If corruption, criminal conduct or serious misconduct is identified, it can explore causes, preconditions, executive government roles and responsibilities, impacts and actions.

A special prosecutor to work in tandem with the commission will be chosen once the office is set up in September, Mr Carroll said.

The premier has come under fire from the state opposition for taking more than three weeks to formally trigger the inquiry.

Mr Carroll said "immediately" establishing the commission and special prosecutor was his first order of business after toppling Jacinta Allan as premier on July 28.

Ms Allan had for months rejected widespread calls to launch a probe into allegations of dodgy dealings within the state's $100 billion infrastructure program, known as the Big Build.

In a report into the Victorian arm of the CFMEU, corruption-busting lawyer Geoffrey Watson SC estimated taxpayers lost $15 billion owing to corruption on state government construction projects.

Mr Carroll, who has served in cabinet since 2017, previously signalled he wanted the commission to begin before the November state election and said he was willing to give evidence if required.