An under-fire Australian minister who accepted an anonymous donation to sue public broadcaster ABC after it published rape allegations against him has resigned, Prime Minister Scott Morrison announced Sunday.

The accusation that an unnamed senior government minister raped a 16-year-old girl in 1988 helped to spark nationwide women's rights protests in March.

Then-attorney general Christian Porter went public to deny the allegations soon after they emerged and was later demoted to a lesser portfolio but remained a key member of the conservative government.

His political future was thrown into doubt last week after he revealed he had accepted funds from a blind trust to pay some of his legal fees in the ABC case, throwing up the possibility of an ethics violation.

Morrison, who had sought advice on whether that was a breach of ministerial standards, said Sunday Porter had resigned to avoid any real or perceived conflict of interest over the unknown donor.

"That is the appropriate decision in these circumstances (and) that reinforces our government's commitment to those standards," Morrison said.

Porter was expected to remain as a member of parliament but will sit on the backbench, the prime minister added.

In a statement to ABC, Porter insisted his disclosure was within the rules, but said the issue had become an "unhelpful distraction for the government".

While he did not receive any damages from the broadcaster after dropping the defamation suit, an editor's note was added to the original article stating the broadcaster had not intended to suggest he committed the criminal offences.

The woman at the centre of the story died in June 2020, reportedly by suicide.

The accusations emerged just weeks after a young government staffer separately alleged she was raped by a colleague in parliament in 2019 and failed by her bosses when she reported the incident. 

The cases spurred tens of thousands of women to take to the streets, calling for gender equality and an end to sexual violence in Australia.

As part of its response, the government has introduced a new parliamentary code of conduct and recently held an online "women's safety summit" that was panned by some advocates as ineffectual.