Former Treasurer Josh Frydenberg, who left politics after losing his seat in the May election, was also unaware Morrison held responsibility for treasury, The Australian newspaper reported.
Liberal Opposition leader Peter Dutton said legal advice from the solicitor general was needed before any decisions on next steps were made.
In a lengthy statement, Morrison, who remains a Liberal backbencher, said he regretted that his actions had caused concern but he had “acted in good faith in a crisis”.
Morrison defended taking on extra ministerial roles without his cabinet’s knowledge during the COVID-19 pandemic, saying it was “an unprecedented time” and that the powers served as a safeguard.
“I used such powers on one occasion only. I did not seek to interfere with Ministers in the conduct of their portfolio,” he said in the statement.
He added that “in hindsight these arrangements were unnecessary.”
Morrison said in a radio interview earlier on Tuesday he didn’t make the arrangements public because they were a safeguard only, and it was an “oversight” the ministers weren’t informed their roles were duplicated.
“We had to take some extraordinary measures to put safeguards in place,” he told radio station 2GB, likening it to having two keys on a nuclear submarine.
The resources minister role he took on in 2021 was different, he said, because he had used the power to stop approval for a gas exploration project off the coast of Australia which was opposed by local communities. The decision is being challenged in court.
“I believe I made the right decision in the national interest. This was the only matter I involved myself directly with in this or any other Department,” he said in the statement.
Albanese said it was concerning that two people had responsibility for the resources portfolio and had different positions on matters.
Not tabling in parliament who was responsible for ministerial portfolios was “a very clear breach of the obligations that the prime minister has to the parliament,” he told ABC radio earlier on Tuesday.