At a court martial near Baghdad airport, Judge Colonel James Pohl also sentenced the army reservist on Thursday to a reduction in rank to private, forfeiture of pay and a dishonourable discharge.
It was the toughest sentence in three convictions to date related to degrading abuses at the Abu Ghraib prison. The abuses were exposed with the publication in April of photographs that outraged the world.
Frederick's lawyer Gary Myers called the sentence excessive and said he intended to appeal to seek a reduction.
The US soldier did not plead guilty to all the elements of the five charges against him during the first of a two-day court martial on a military base at Baghdad's international airport.
Staff Sergeant Frederick offered a rare insight into what went on in the detention centre where pictures of grinning US soldiers posing by a heap of naked Iraqi men taken earlier in the year sparked worldwide outrage.
The extent of the alleged abuse became even more apparent when one of the prisoners testified, describing being hit and humiliated to the point of wanting to die.
US dailies came out with the first
pictures of abuse at Abu Ghraib
Referring to a photograph of a pyramid of seven inmates - one of the most notorious images from the Abu Ghraib outrage - Frederick, the highest-ranking soldier accused in the affair, said they were criminal suspects who had been hooded and their hands tied.
"We threw them in a pile," he told the trial judge.
"That's when Sergeant [Javal] Davis started jumping in the pile," he said referring to one of two other soldiers due to appear in court this week.
Frederick said Davis had been "sort of" laughing as he stomped on the prisoners' hands and feet, and admitted that he could have stopped the abuse. "But I didn't," he said.
Instead, the military policeman joined in as the detainees were stripped and abused, punching one of them, he added.