Private Bradley Manning has been sentenced to 35 years in prison for providing classified US diplomatic and military files to WikiLeaks.
He was convicted in July of 20 charges, including espionage.
Last week, Manning apologised for hurting the United States and for the ''unexpected'' results of his actions.
Prosecutors had asked for a sentence of 60 years in order to send a message to future potential leakers.
Judge Colonel Denise Lind also said Manning would be dishonorably discharged from the US military and forfeit his pay.
The BBC reports Private Manning will receive a credit against his sentence of 3½ years, including time he has already served in jail and 112 days in recompense for the harsh conditions of his initial confinement.
He could be eligible for parole in about 11 years.
While stationed in Iraq in 2010, the junior intelligence analyst passed more than 700,000 documents, including an estimated 250,000 diplomatic cables, to Wikileaks.
Manning has said he leaked the secret files in the hopes of sparking a public debate about US foreign policy and the military.
In a statement during the sentencing hearing, he told the court martial at Fort Meade, Maryland he mistakenly believed he could change the world for the better, and that in retrospect, he should have worked "inside the system".
The BBC reports Manning was arrested in May 2010 in Iraq. He is expected to serve his sentence at Fort Leavenworth, Kansas.
Defence lawyer David Coombs has asked President Barack Obama to pardon his client.
Amnesty International also announced an online petition asking President Obama to pardon him.