The parade by Portadown District Orange Order is due to start at 13:00 BST at Drumcree church on Sunday and finish at Carleton Street in the town centre by 14:30.
A total of 60 people would march along the road in silence, without any bands.
The last time the commission considered the parade route, it re-routed the march, but that decision in June was later quashed in court as proper procedures had not been followed.
The commission’s decision, known as a determination, was explained in a nine-page document.
A lengthy explanation is expected to accompany the latest determination.
The decision could face a legal challenge. The reasons behind the determination are likely to be outlined in detail.
Final submissions were made this week by the Orange Order and the Garvaghy Road Residents Coalition as well as all of the major political parties in Northern Ireland.
The police were also consulted about the planned parade.
The Police Service of Northern Ireland says it has activated “mutual aid arrangements to support contingency planning for a policing operation” in Portadown on Sunday.
The Parades Commission, led by Professor Evelyn Collins, has been in the political spotlight since its previous Drumcree determination was quashed in the High Court.
A review of the commission has since been ordered by the Northern Ireland Office.