Police Minister Paul Papalia will add the corrective services portfolio to his responsibilities, replacing Bill Johnston after a tumultuous period of riots and claims of human rights violations in youth detention.
Mr Johnston is to remain minister for energy, adding the hydrogen industry portfolio.
In an otherwise minor reshuffle, Mr Cook confirmed his deputy Rita Saffioti will become treasurer in addition to retaining the high-spending transport portfolio.
She will shed planning and ports, the latter to be overseen by sole newcomer David Michael who also takes on local government and road safety.
The new-look cabinet will be sworn in on Thursday, formalising Mr Cook's rise to the top job following Mark McGowan's shock retirement, with the next election in 2025.
"This is the team we're taking to the grand final, pending extraordinary circumstances," Mr Cook told reporters on Wednesday.
"We are getting on with the job.
"It's a government with renewed energy, with renewed focus."
Mr Papalia spent eight years as opposition spokesman for corrective services before Labor came to power in 2017 and is set to be tasked with balancing community safety with a renewed focus on rehabilitation for youths in detention.
"He was the architect of our justice reinvestment policies in opposition so I now want him to continue that work," Mr Cook said.
"I'll be working with Paul in this important policy area to make sure that we can provide a fresh set of eyes ... he has the commitment, the courage and he will be able to take that policy area forward very effectively."
Ms Saffioti's dual roles will mean she is responsible for maintaining the government's fiscal discipline while also dealing with cost blowouts and delays to major infrastructure projects including the $10 billion Metronet train network.
She insisted the expenditure review committee process would ensure accountability for spending decisions and was confident she had the energy to manage both roles.
"Former treasurers have also held high-spending portfolios, so this is nothing new," she said.
"The treasurer doesn't just write cheques for their own agencies."
Finance Minister Sue Ellery kept her post despite having already confirmed she won't contest the 2025 election.
Speculation remains over whether Mr Johnston and Attorney-General John Quigley will also retire.
Amber-Jade Sanderson retained the health portfolio after her failed challenge for the Labor leadership revealed rifts within the dominant left faction.
With Mr McGowan's retirement offering renewed hope to the decimated Liberals and Nationals in opposition, his successor pledged to lead an economically strong and socially progressive government.
"This is a team that is united, experienced, hungry and hard-working," he said.
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