In his first statements at the court martial, Manning confirmed he pleads guilty to 10 charges but not the most serious one against him - aiding the enemy - which could see him spend the rest of his life in jail.
More than three years after he was arrested in Iraq, the baby-faced 25-year-old US army private went before a court martial presided over by Judge Denise Lind at a military base outside Washington, DC.
Security was ultra tight, with a gaggle of US and foreign reporters waiting in line for two hours to get through security checks and into the courtroom, where cell phones and other electronic devices were banned.
From November 2009 until his arrest in May 2010, Manning allegedly gave WikiLeaks some 700,000 classified military logs from Iraq and Afghanistan and diplomatic cables from across the world.
He faces a possible 154-year jail sentence. Manning has offered to plead guilty to several offenses but denies prosecutors' most serious charge - that he knowingly aided the enemy, chiefly al Qaeda.
Manning's supporters view him as a whistle-blower, and as a steady rain fell outside the base Monday morning around 30 demonstrators waved banners that read "Bradley Manning, hero" and shouted "Free Bradley."
The trial went into recess after Manning confirmed his guilty plea to the 10 charges, said he wanted to be tried by Lind and a not a jury, and signed requests for witnesses to testify.
The government and the defense were to make preliminary statements, and testimony from investigators and Manning's roommate in Iraq were scheduled for later in the day.
The proceedings follow an exhaustive series of preliminary hearings that outlined the government's case against Manning.
The government accuses Manning of having endangered national security by releasing the war logs, which included reports of torture and civilian casualties, and the embassy cables, which detailed candid and often embarrassing remarks by world leaders and US officials.
The soldier's supporters argue his actions shone a light in the darkest corners of the US-led wars in Iraq and Afghanistan, as well as exposing the reasoning behind American foreign policy decisions.
Judge Lind has warned she will not allow Manning's trial to turn into a forum on US foreign policy.
Among other leaks, Manning admitted to the "willful transmission" of a video that showed a US combat helicopter shooting at Iraqi civilians in July 2007.
Dubbed "collateral murder" by WikiLeaks, the video was made public by Julian Assange's organization in April 2010.
The soldier also acknowledged transmitting a confidential video of a US air strike on the Afghan village of Granai, where more than a hundred civilians lost their lives in May 2009.
The lengthy nature of the proceedings against Manning - arrested while serving as a military intelligence analyst near Baghdad - has revolved around the complexity of the charges he faces and his treatment in custody.
His defense team successfully argued that he had been subject to unduly harsh detention methods from US military personnel and, consequently, he will receive a 112-day reduction of any eventual jail sentence.
Manning admitted in February to leaking the documents, saying he hoped to start a public debate, but denied knowingly aiding al Qaeda or other US foes.
Manning has offered to plead guilty to 10 offenses, including breaches of military discipline and good conduct, which could see him sentenced to 20 years.
However, he could face a maximum of 154 years in jail if found guilty of the more serious charges, including that of "aiding the enemy."
Part of the US government's case against Manning asserts that the late al Qaeda leader Osama Bin Laden had asked an aide to retrieve documents from the Internet that the soldier had passed to WikiLeaks.
A Navy SEAL who participated in the May 2011 raid that killed Bin Laden at his hideout in Pakistan is expected to testify, as are dozens of other witnesses.
The trial is expected to last 12 weeks. Some evidence will be given behind closed doors for national security reasons.
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Evidently ,speaking the truth is a grave crime in the US of A don't ya know - the land of the free .. so If this is how they treat their own citizens and then criticise other nations for alleged human right abuses says a lot about their credibility and how they deal with their dissidents The only nation on earth that is war-mongering and war-waging all around the world whether covertly or overtly on a year on year basis is the one with the big guns- the US of A . It's NOT defending itself against any terrorist entity. Rather IT IS the biggest terrorist state of them all along with is allies killing countless innocents and spreading terror and destruction to destabilise the developing world in order to keep a stranglehold and monopoly of the worlds resources ,This IS all about American foreign policy which IS open for debate. Denying the real issues will not make the facts and evidence that Bradley Manning and Wikileaks exposed go unaccounted for. But don't expect any justice from Judge LInd. They will make an example of Mr Manning of what happens to Americans if they dare to be disloyal to their foreign policy never mind that it perpetuates injustice and creates more enemies/
It appears that in actuality Mr. Manning has been charged with telling the truth. We cannot have that can we?