The loyal orders are to mark the 500th anniversary of the Reformation with what it anticipates will be one of the largest and most significant public events in Europe.
Thousand of members of the Orange and Royal Black Institutions will participate in a procession through Portadown this weekend, followed by an open-air religious service.
They will be joined in the Co Armagh town by the Apprentice Boys, the Association of Loyal Orange Women of Ireland, the Independent Orange Institution, the Grand Royal Arch Purple Chapter and the Junior Association.
Saturday's parade, incorporating upwards of 60 marching bands, is the flagship event of the Luther 500 project, organised by the Loyal Orders.
The rally comes ahead of the actual 500th anniversary of the start of the Reformation, later this year. In October 1517, Martin Luther nailed his '95 Theses' on the castle door in Wittenberg in Germany - an act widely seen as the beginning of the Protestant Reformation, which spread throughout Europe.
The Grand Master of the Grand Orange Lodge of Ireland, Edward Stevenson, said: "We hope this event will be an impressive expression of our Institution's Christian ethos as we come together with members of the other Loyal Orders to collectively convey our faith, and remember and celebrate one of the most momentous events in history, five centuries ago.
"For its part, the Orange Institution is proud to commemorate such an evangelical milestone through such gospel witness, and we very much look forward to partaking in the religious service at Shamrock Park."
The Sovereign Grand Master of the Royal Black Institution, Millar Farr, added: "In this decade of centenaries, and as a Protestant fraternity, we recognise the need to commemorate such an important evangelical landmark. I would encourage all of our members to make every effort to attend this iconic event to celebrate the Reformation."
Both leaders will pay their respects at the town cenotaph in memory of those who lost their lives during two World Wars and in service of the British Crown.
The main parade is scheduled to leave Edenderry at 5.15pm and will proceed via Bridge Street, High Street, Market Street, Church Street, Armagh Road and Brownstown Road to the rally venue at Shamrock Park.
The parade will pause at the Bann Bridge as a wreath is laid to commemorate those Protestants killed in the 1641 Portadown massacre.