The eight, including two officers, fought in Iraq as part of the First Marine Division during the campaign to topple the Saddam Hussein government.
Defence and justice officials said on Saturday the reservists were detailed to guard a prisoner of war camp called Camp Whitehorse outside the southern city of Nasiriya.
Marine spokesman Staff Sergeant Bill Lisbon said the charges ranged from negligent homicide to assault and dereliction of duty.
All eight have now been moved to Camp Pendleton, a Marine Corps base outside San Diego, California, where they are going through various pretrial hearings, Lisbon said.
The homicide and other charges were formally filed on Thursday, but no date for a court martial has been set.
Military prosecutors allege that an Iraqi man named Najim Sadun Hatab died at Camp Whitehorse in early June, following a possible beating by US guards. Details of the incident remain unclear.
The most serious and sweeping accusations are being levelled against Major Clark Paulus.
He has been charged with negligent homicide, assault, cruelty and maltreatment, dereliction of duty and making false statements, Lisbon said.
The other officer involved in the case, Major William Vickers, faces one count of dereliction of duty, he said.