Bradley Manning has admitted for the first time that he was responsible for the biggest leak of government secrets in US history, after he supplied vast amounts of classified material to the Wikileaks website. In a court martial hearing at Fort Meade, Maryland on Thursday, Manning pleaded guilty to 10 of the 22 charges of which he is accused, though he plans to fight the most serious charge, of aiding the enemy.

Appearing before military judge Colonel Denise Lind, The 25-year-old Army Intelligence Private waived his right to a jury trial, in favour of being tried by a judge alone. It is thought he pleaded guilty to the lesser offences so as to be given the opportunity to explain his actions and motivations – an opportunity previously denied to him in the more than 1,000 days since he was arrested in Iraq in May 2010.

Dressed in full uniform, Manning testified that he had passed classified material to Wikileaks because he believed, “if the general public... had access to the information... this could spark a domestic debate as to the role of the military and foreign policy in general.”

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Speaking under oath for more than an hour, he explained that he had first tried to pass the files to The Washington Post, The New York Times and Politico, but that none had taken him seriously. He spoke to a reporter at the Post, and left a voicemail message for the ombudsman of the New York Times, which was never returned. He tried to visit Politico’s Washington DC office, he said, but was thwarted by “weather conditions”, and so turned instead to the Wikileaks website, beginning a lengthy online exchange with a Wikileaks member who went by the web pseudonym “Ox”, and whom he now believes was the site’s controversial founder, Julian Assange.

According to journalists at the base, who watched the court proceedings via a live feed, Manning said he chose to leak documents that he believed would be embarrassing to the US, but would not harm national security. “I wanted the American public to know that not everyone in Iraq and Afghanistan was a target that needed to be engaged and neutralised,” said Manning, suggesting that he had "accomplished something that would allow me to have a clear conscience.”

The Private was allowed to read aloud from his 35-page explanatory statement, only the second time he has been permitted to speak in public since his arrest. In November 2012, he told a court about the harsh conditions of his imprisonment at Quantico marine base in Virginia. For months, he was held in solitary confinement for 23 hours per day and kept on suicide watch, which called for regular naked inspections, and obliged him to sleep without darkness or bedclothes. In January, Judge Lind ordered that any sentence handed down to Manning be reduced by 112 days to reflect the illegal pre-trial treatment he was forced to endure.

Manning will admit at his court martial to having leaked classified documents including those relating to the US detention camp at Guantanamo; Iraq and Afghanistan war logs; State Department Cables; Department of Defence memos; and the so-called “Collateral Murder” video, which shows the death of Reuters journalist Namir Noor-Eldeen and several others in Baghdad, in a 2007 attack by a US Apache helicopter.

Manning said he was “horrified” by the apparent bloodlust of the US military personnel heard communicating in the clip, which thrust Wikileaks to the forefront of the public consciousness when it was posted online in April 2010. The site’s subsequent steady release of classified US government documents throughout that year, in conjunction with newspapers including The New York Times, was based on the data allegedly leaked by Manning.

The disclosures shocked the public, spelled humiliation for many diplomats and, claimed outraged US officials, endangered the lives of Americans and their confidential sources in Afghanistan and elsewhere. His prosecutors claim that Manning “indirectly” abetted Al Qaeda by making such information public. Yet Manning’s supporters also say his exposure of corruption in many governments helped to set off the Arab Spring.

In the years since Manning was jailed, Wikileaks itself has suffered a series of high-profile internal disputes and defections. After he was accused of alleged sex crimes in Sweden in August 2010, Assange spent 10 days in Wandsworth Prison, before being placed under house arrest at Ellingham Hall in Norfolk. In June last year, apparently fearing extradition to Sweden, and thence to the US, he sought asylum at the Ecuadorean embassy in London, where he has remained ever since.

Manning faces a maximum of 20 years in prison for the 10 lesser charges to which he pleaded guilty, which include unauthorized possession and wilful communication of information from military databases, including the Combined Information Data Network Exchange Iraq and Combined Information Data Network Exchange Afghanistan. If convicted of the headline charge of aiding the enemy, however, he could be sentenced to life imprisonment. His trial is due to commence on 3 June.

Manning's full statement can be read by clicking here