In addition to the prison sentence, Specialist Glendale C Walls was on Tuesday reduced in rank and pay and will receive a bad-conduct discharge.
Walls pleaded guilty earlier in the day to dereliction of duty and assault. He admitted that he stood by as former Sergeant Selena M Salcedo lifted a detainee known as Dilawar by his ear when the two worked at Bagram Airfield in Afghanistan.
Walls also admitted to pushing Dilawar against a wall during the interrogation.
He said he also stood by as a third military intelligence soldier, former Specialist Joshua R Claus, made another detainee roll around on the floor and kiss Walls' boots.
Dilawar was detained during December 2002 and died the same month.
Pay cut sought
Prosecutors had sought a sentence of six months' confinement, a six-month, 75% pay cut, the demotion and the bad-conduct discharge.
The maximum sentence Walls could have faced was 12 months confinement, a 75% pay cut for 12 months, a reduction in rank and a bad-conduct discharge.
Walls' attorney asked for a letter of reprimand and reduction in rank.
The Afghan detainee in question
died in December 2002
Salcedo pleaded guilty to similar charges this month. Tearfully apologising for her conduct, she told a military judge that Walls was with her when she mistreated Dilawar and that Walls had pushed Dilawar.
Salcedo will be demoted, given a letter of reprimand and ordered to forfeit $250 a month for four months.
Claus has announced his intention to plead guilty in the abuse cases and is scheduled to stand trial in September.
At least six other enlisted soldiers have been accused of mistreating Dilawar a little more than a week after arriving at the detention centre in Bagram.
The most serious charges were levied against Private First Class Willie V Brand, a reservist and military police officer, who initially was charged with Dilawar's death.
A military jury convicted Brand last week of assault, maltreatment, maiming and making a false official statement.
The same jury spared Brand jail time, instead ordering that he be reduced in rank and pay to a private, the army's lowest rank.
Bagram has served as a US base
since the post-9/11 invasion
Specialist Brian E Cammack pleaded guilty in May to abuse charges and was sentenced to three months in prison.
Cammack testified against Brand.
Sergeant James P Boland, also a reservist from Ohio, was given a letter of reprimand citing him for dereliction of duty for his work at Bagram.
Boland, who has left the army, was initially charged with chaining Dilawar's hands above his head and other abuse charges.