John Anthony Downey, 61, of Co Donegal, was arrested at Gatwick Airport in May.
He is accused of being responsible for a car bomb left in South Carriage Drive which killed the soldiers as they rode through the park to the changing of the guard.
The explosion injured other members of the Royal Household Cavalry and killed seven horses as they travelled from their barracks to Buckingham Palace.
Downey is charged with murdering Roy Bright, Dennis Daly, Simon Tipper and Geoffrey Young, and with intending to cause an explosion likely to endanger life.
He is due to stand trial at the central London court next year.