13/02/2016 1:29 PM AEDT | Updated 15/07/2016 12:51 PM AEST

Mal Brough Resigns From Turnbull Ministry

Stefan Postles via Getty Images
CANBERRA, AUSTRALIA - DECEMBER 03: Special Minister of State Mal Brough during House of Representatives question time at Parliament House on December 3, 2015 in Canberra, Australia. Mr Brough is being investigated by the Australian Federal Police any involvement in getting former staffer James Ashby to obtain copies of then-speaker Peter Slipper's diary in 2012. (Photo by Stefan Postles/Getty Images)

Mal Brough has resigned from the federal government's front bench ahead of Prime Minister Malcolm Turnbull's cabinet shuffle.

Brough said he was resigning from the ministry after becoming aware an Australian Federal Police (AFP) investigation into his conduct regarding the diary of former parliamentary speaker, Peter Slipper, would take months to complete.

"I said to him that 'Prime Minister, in the event I'm now of the knowledge it's going to take several months for the AFP to conclude its inquiry that it's not appropriate to keep open my two portfolios and hence, I would like to notify you of my resignation'," Brough told reporters on Saturday.

"I do this in the interests of what is in the best interests of the nation and the nation deserves to have all the ministry positions filled and so the public can understand who they're voting for."

The resignation leaves open the Special Minister of State position in Turnbull's cabinet, which is expected to be filled later today.

Brough stood aside as Special Minister of State in December after becoming embroiled in a saga over the alleged copying of Slipper's diary.

At the time, Turnbull said Brough had done the right thing in standing aside "recognising the importance of the government maintaining an unwavering focus on jobs, economic growth and national security".

Brough, who was also Defence Materiel and Science Minister, will now be replaced on the front bench.