A federal tribunal has ordered Prime Minister Scott Morrison’s department to release secret documents about the workings of national cabinet after rejecting government claims the peak group is a committee of federal cabinet.

The tribunal backed an appeal from independent senator Rex Patrick in a significant decision that opens national cabinet to public scrutiny through requests for its agendas, minutes and other documents.

The ruling also shatters government claims the peak group, led by Mr Morrison with state premiers and territory chief ministers, has the status of a committee of federal cabinet and is therefore shielded from scrutiny.

Senator Patrick hailed the outcome on Thursday night as a “decisive win for transparency and accountability” because it rejected Mr Morrison’s attempts to claim a protection for national cabinet that it did not deserve under the law.

The South Australian senator took his claim to the Administrative Appeals Tribunal after the Department of Prime Minister and Cabinet rejected his applications under the Freedom of Information Act for documents about national cabinet meetings.