Australia is set to bring in new laws to increase transparency after a report savaged the former prime minister for giving himself secret roles.
Scott Morrison - who was defeated at an election this year - has defended his appointments to several ministries as "necessary" in "extraordinary times".
But an inquiry by a former High Court justice found his conduct was "corrosive of trust in government".
And current PM Anthony Albanese says it was "unprecedented and inexcusable".
It emerged in August this year that Mr Morrison had become joint minister for health, finance, treasury, home affairs and resources in the two years before he lost power in May.
Most ministers were reportedly unaware they were sharing portfolios with Mr Morrison and he has been widely criticised, including by close colleagues.
Mr Morrison only used his extra powers once, to overrule the resources minister in a matter unrelated to the pandemic.
An investigation by the solicitor-general early this year found Mr Morrison had acted legally but had "fundamentally undermined" responsible government.
After a three-month inquiry, Virginia Bell came to a similar conclusion.
She ultimately found the appointments were "unnecessary" and three of five had "little if any connection to the pandemic".
Mr Morrison's rationale for swearing himself in to the ministries was "not easy to understand and difficult to reconcile," she added.
The report also revealed that Mr Morrison also instructed his department to plan for his appointment to administer a sixth additional role, but ultimately decided not to proceed with it.
The report does not criticise Australia's governor general who oversaw the secret appointments, saying he was acting on the advice of the government of the day.
Mr Morrison on Friday repeated his defence of his actions, in a statement posted on social media.
"These decisions were taken during an extremely challenging period, where there was a need for considerable urgency," he said, noting critics were speaking with the "benefit" of hindsight.
He questioned the ability for "third parties" to draw "definitive conclusions" on the matter.
But Mr Albanese said report showed that the actions of the former prime minister were "extraordinary" and "wrong", adding the previous government had operated under a culture of secrecy.
He said the Australian people were owed an apology after being "misled over the structure of their government".
Mr Albanese accepted the report's suggestions for reform, including new legislation that would require any appointments be publicly disclosed.
Earlier on Friday morning, former Treasurer Josh Frydenberg spoke out for the first time, saying Mr Morrison's secret ministries were "extreme overreach".
Mr Morrison was a close political ally and still hasn't apologised for secretly swearing himself into the treasury portfolio, Mr Frydenberg - who lost his seat at the election - has told columnist and author Niki Savva.