Judge Colonel Denise Lind, who last month found Manning guilty of 20 charges, including espionage and theft, could have sentenced him to as many as 90 years. Prosecutors had asked for 60 years.
Manning, 25, will be dishonorably discharged from the US military and forfeit some pay, Colonel Lind said. His rank will be reduced to private from private first class.
Manning will be eligible for parole after serving one-third of his sentence, which will be reduced by the time he has already served in prison plus 112 days.
WikiLeaks said the 35-year jail term was a "strategic victory" because it meant Manning was eligible for parole in less than nine years.
Wearing his dress uniform, slightly-built Manning stood at attention as the sentence was read, seeming to show no emotion. As he was escorted out of the courtroom, supporters shouted "Bradley, we are with you."
Manning spent his teenage years in Wales and an uncle there, Kevin Fox, said he had mixed feelings about his nephew's sentencing.
He said : "It was less time than I thought - that's got to be a good thing. I hope it will be reduced (in the future). But, to be honest, he shouldn't have been given any time at all. In my eyes he is a hero."
Elizabeth Goitein, co-director of the Liberty And National Security Programme at the Brennan Centre For Justice, called the sentence "unprecedented" in its magnitude.
She said it was more than 17 times the next longest sentence ever served for providing secret material to the media and added: "It is in line with sentences for paid espionage for the enemy."
As a low-level intelligence analyst, Manning had access to a large amount of very sensitive information, despite his junior rank, and was deployed to Baghdad, Iraq, in 2009.
In 2010, he turned over more than 700,000 classified files, battlefield videos and diplomatic cables to WikiLeaks in a case that has commanded international attention, also catapulting the website and its founder Julian Assange into the international spotlight.
The classified material that shocked many around the world included a 2007 gunsight video of a US Apache helicopter firing at suspected insurgents in Baghdad. Among the dozen fatalities were two Reuters news staff.
The case highlighted the difficulty in keeping secrets in the internet age. It raised strong passions on the part of the US government - which said Manning had put American lives at risk - and anti-secrecy advocates, who maintained Manning was justified in releasing the information.
During a pre-trial hearing, Col Lind had determined the eventual sentence would be reduced by 112 days because of harsh treatment after Manning's arrest in 2010. He is likely to be imprisoned at the US Disciplinary Barracks at Fort Leavenworth, Kansas.
A US rights group has said Manning should be a candidate for this year's Nobel Peace Prize, while Amnesty International called on US President Barack Obama to commute Manning's sentence.
Widney Brown, Amnesty's senior director of international law and policy, said: "Instead of fighting tooth and nail to lock him up for the equivalent of several life sentences, the US government should turn its attention to investigating and delivering justice for the serious human rights abuses committed by its officials in the name of countering terror."
Manning's trial at Fort Meade, Maryland, home of the National Security Agency, wound down as US officials sought his fellow whistleblower Edward Snowden, a former NSA contractor, who has been granted asylum in Russia