The sentencing on Saturday by a military jury at a Texas army base came a day after Graner was found guilty on 10 counts related to the abuses, including stacking naked prisoners into a pyramid.
Graner showed no reaction when the sentence was read and appeared calm before he was taken off to prison.
Asked if he regretted abusing prisoners, Graner paused, then said: "Maybe you missed that there's a war. Bad things happen in war.
"Apparently I followed an illegal order."
In his first public remarks on the scandal earlier in the day, Graner told the 10 jurors that he had acted wrongly, but said he complained repeatedly to superiors and was told to continue rough treatment.
In his testimony at the sentencing hearing, Graner smiled from time to time and spoke confidently as he detailed his role in the scandal.
Graner now admits what he did
was wrong and criminal
"I didn't enjoy anything I did there. A lot of it was wrong, a lot of it was criminal," Graner, 36, admitted.
"The enemy needs rallying points," prosecutor Major Michael Holley said in arguing for the maximum 15-year penalty. "The accused has provided so much in that regard."
Graner also received a dishonourable discharge and forfeiture of all pay and allowances.
Graner, seen grinning in photos of abuses such as stacking a pyramid of naked Iraqi prisoners, said gallows humour was the only way to deal with the harsh environment at Abu Ghraib.
"There was a lot of things that we did that were so screwed up, if we didn't look at them as funny then there was no way to deal with it," he said. "When I knew someone would take a picture, I would be smiling, that's the only explanation I have."
Graner said he complained repeatedly to superiors about the rough treatment.
"We were not treating prisoners the way we were supposed to so I complained about it," he said. "I never stopped complaining."
Graner named several higher-ranking officials to whom he complained about the conditions or treatment forced upon prisoners, such as sleep deprivation and forced eating cycles. They told him to "follow your order, charge on".
"Like all good soldiers, or bad little soldiers, it was right on, sir. We went back."