An incident, commonly referred to as Cablegate, began on 28 November 2010 when WikiLeaks began releasing classified cables that had been sent to the U.S. State Department by 274 of its consulates, embassies, and diplomatic missions around the world. Dated between December 1966 and February 2010, the cables contain diplomatic analysis from world leaders, and the diplomats' assessment of host countries and their officials.

On 30 July 2013, Chelsea Manning was convicted for theft of the cables and violations of the Espionage Act in a court martial proceeding and sentenced to thirty-five years imprisonment. She was released on 17 May 2017, after seven years total confinement, after her sentence had been commuted by President Barack Obama earlier that year.

The first document, the so-called Reykjavik 13 cable, was released by WikiLeaks on 18 February 2010, and was followed by the release of State Department profiles of Icelandic politicians a month later. Later that year, Julian Assange, WikiLeaks' editor-in-chief, reached an agreement with media partners in Europe and the United States to publish the rest of the cables in redacted form, removing the names of sources and others in vulnerable positions. On 28 November, the first 220 cables were published under this agreement by El País (Spain), Der Spiegel (Germany), Le Monde (France), The Guardian (United Kingdom), and The New York Times (United States). WikiLeaks had planned to release the rest over several months; 2,017 had been published as of 11 January 2011.^{[citation needed]}

The remaining cables were published in September 2011 after a series of events compromised the security of a WikiLeaks file containing the cables. This included WikiLeaks volunteers placing an encrypted file containing all WikiLeaks data online as "insurance" in July 2010, in case something happened to the organization. In February 2011 David Leigh of The Guardian published the encryption passphrase in a book; he had received it from Assange so he could access a copy of the Cablegate file, and believed the passphrase was a temporary one, unique to that file. In August 2011, German weekly Der Freitag published some of these details, enabling others to piece the information together and decrypt the Cablegate files. The cables were then available online, fully unredacted. In response, WikiLeaks decided on 1 September 2011 to publish all 251,287 unedited documents.

The publication of the cables was the third in a series of U.S. classified document leaks distributed by WikiLeaks in 2010, following the Afghan War documents leak in July, and the Iraq War documents leak in October. Over 130,000 of the cables are unclassified, some 100,000 are labeled "confidential", around 15,000 have the higher classification "secret", and none are classified as "top secret" on the classification scale.

In June 2010, the magazine Wired reported that the U.S. State Department and embassy personnel were concerned that Chelsea Manning, a United States Army soldier charged with the unauthorized download of classified material while stationed in Iraq, had leaked diplomatic cables. WikiLeaks rejected the report as inaccurate: "Allegations in Wired that we have been sent 260,000 classified U.S. embassy cables are, as far as we can tell, incorrect".

However, during that same month (June 2010), The Guardian had been offered "half a million military dispatches from the battlefields of Afghanistan and Iraq. There might be more after that, including an immense bundle of confidential diplomatic cables", and Alan Rusbridger, the editor of The Guardian had contacted Bill Keller, editor of The New York Times, to see if he would be interested in sharing the dissemination of the information.

Manning was suspected to have uploaded all that was obtained to WikiLeaks, which chose to release the material in stages so as to have the greatest possible impact.