Bradley Manning was sentenced on Wednesday to serve 35 years in a military prison for turning over more than 700,000 classified files to WikiLeaks.
It has been called the biggest breach of secret data in the nation's history.
Judge Colonel Denise Lind sentenced the 25-year-old low-level intelligence analyst to less time than the 60 years military prosecutors had sought.
Manning could have been given up to 90 years, some experts believed, but will be eligible for parole in a decade, after serving one-third of his term.
Even that shorter prison term is seen as a strong deterrent to others who may consider exposing U.S. government secrets, according to analysts.
Elizabeth Goitein, a transparency advocate and co-director of the Liberty and National Security Program at the Brennan Center for Justice, said:
"It's more than 17 times the next-longest sentence ever served."
"It is in line with sentences for paid espionage for the enemy."
Bradley Manning, in uniform, stood quietly showing no emotion as Lind read his sentence during a brief court proceeding at Fort Meade, Maryland.
Lind said Manning would be demoted to private, from private first class, and dishonorably discharged from the U.S. military on top of the sentence.
Also, that his sentence would be reduced by the three years he has served in prison, plus the 112 days she had already decided to subtract.
That amount was deducted because of the harsh treatment that the soldier suffered immediately after his arrest three years ago, the judge ruled.