Mal Brough has formally resigned from the front bench ahead of Prime Minister Malcolm Turnbull's major reshuffle expected to be announced on Saturday.
He had stood aside as Special Minister of State just after Christmas pending a federal police investigation into the copying of Peter Slipper's official diaries when he was Speaker.
Mr Brough, who was also defence materiel and science minister, will now be replaced on the front bench.
Mr Brough told Mr Turnbull earlier on Saturday that he would resign because "it's going to take several months for the AFP to conclude its inquiry."
"The nation deserves to have all the ministry positions filled and so the public can understand who they're voting for," he told reporters.
Finance Minister Mathias Cormann and Defence Minister Marise Payne had been covering Mr Brough's portfolios since his suspension on December 29.
Mr Brough has been facing a police investigation into whether he asked Mr Ashby, a former staffer of Mr Slipper, to copy the former Speaker's diary.
He's denied any wrongdoing, despite telling the Nine Network last year he asked Mr Ashby to procure copies of the diary.
Mr Brough stood aside the same day Jamie Briggs resigned as cities minister.
