In June 2013, while at The Guardian, he began publishing a series of reports detailing previously unknown information about American and British global surveillance programs based on classified documents provided by Edward Snowden.

[13][14] He worked pro bono much of the time, and his cases included representing white supremacist Matthew Hale in Illinois, who, Greenwald believed, was wrongly imprisoned,[23] and the neo-nazi National Alliance.

[25] Later, according to Greenwald, "I decided voluntarily to wind down my practice in 2005 because I could, and because, after ten years, I was bored with litigating full-time and wanted to do other things which I thought were more engaging and could make more of an impact, including political writing.

[28][29][30][31][32][33] In a 2010 article for Salon, Greenwald described U.S. Army Private Chelsea Manning as "a whistle-blower acting with the noblest of motives" and "a national hero similar to Daniel Ellsberg".

News reported that in 2017, after the publication of the Vault 7 files, "top intelligence officials lobbied the White House" to designate Glenn Greenwald as an "information broker" to allow for more investigative tools against him, "potentially paving the way" for his prosecution.

[52] In a statement delivered before the National Congress of Brazil in early August 2013, Greenwald testified that the U.S. government had used counterterrorism as a pretext for clandestine surveillance to compete with other countries in the "business, industrial and economic fields".

[53][54] On December 18, 2013, Greenwald told the Committee on Civil Liberties, Justice and Home Affairs of the European Parliament that "most governments around the world are not only turning their backs on Edward Snowden but also on their ethical responsibilities".

[55] Speaking via a video link, Greenwald said: "It is the UK through their interception of underwater fibre optic cables, that is a primary threat to the privacy of European citizens when it comes to their telephone and emails".

Greenwald, along with his colleagues Laura Poitras and Jeremy Scahill, initially were working on creating a platform online to support independent journalism, when they were approached by Omidyar, who was hoping to establish his own media organization.

[65] On October 29, 2020, Greenwald resigned from The Intercept, giving his reasons as political censorship and contractual breaches by the editors, who he said had prevented him from reporting on allegations concerning Joe Biden's conduct with regard to China and Ukraine and had demanded that he not publish the article in any other publication.

[72] System Update consists of a monologue concerning topical political issues, often related to media criticism and developments within the American security state, as well as interviews with guests.

Such guests have included academics, political figures, and journalists Jeffrey Sachs, John Mearsheimer, Edward Snowden, Robert F. Kennedy Jr., Lee Fang, and Matt Taibbi, among others.

The messages implicated members of Brazil's judiciary system and of the Operação Lava-Jato taskforce, including former judge and Minister of Justice Sergio Moro, and lead prosecutor Deltan Dallagnol, in the violation of legal and ethical procedures during the investigation, trial and arrest of former president Luiz Inácio Lula da Silva, with the alleged objective of preventing him from running for a third term in the 2018 Brazilian general election, among other crimes.

Following the leak, Folha de São Paulo and Veja confirmed the authenticity of the messages and worked in partnership with The Intercept Brasil to sort the remaining material in their possession before releasing it.

[80] A New York Times profile by Ernesto Londoño about Greenwald and his husband David Miranda, a left-wing congressman, described how the couple became targets of homophobia from Bolsonaro supporters as a result of the reporting.

It describes his publication in 2019 of leaked telephone calls, audio and text messages related to Operation Car Wash and the retaliation he received from Jair Bolsonaro's government.

[105] Tamsin Shaw wrote in The New York Review of Books in September 2018: "Greenwald has repeatedly, in the face of overwhelming evidence to the contrary, decried as Russophobia the findings that Putin ordered interference in the 2016 US presidential election".

[106] Greenwald remained doubtful of assertions that the Trump presidential campaign worked with the Russians after the release of the letter about the Mueller's findings from attorney general William Barr in late March 2019.

[107] Greenwald told Tucker Carlson on Fox News: "Let me just say, [MSNBC] should have their top host on primetime go before the cameras and hang their head in shame and apologize for lying to people for three straight years, exploiting their fears to great profit".

[112][113] In May 2016, Greenwald accused The New York Times of "abject cowardice" in its use of quotation marks for the occupation of Gaza and alleged "journalistic malfeasance" in the incident "out of fear of the negative reaction by influential factions".

[114][115] Following the Charlie Hebdo murders in January 2015, David Bernstein in the Washington Post wrote that Greenwald (in an Intercept article) "certainly appears to believe that Der Stürmer-like anti-Semitic cartoons are the moral and logical equivalent of making fun of Moses or Muhammed".

[116] In a November 2018 Guardian article, Luke Harding and Dan Collyns cited anonymous sources which stated that Trump's former campaign manager Paul Manafort held secret meetings with WikiLeaks founder Julian Assange inside the Ecuadorian embassy in London in 2013, 2015, and 2016.

[118] Greenwald, a former contributor to The Guardian, stated that the paper "has such a pervasive and unprofessionally personal hatred for Julian Assange that it has frequently dispensed with all journalistic standards in order to malign him.

Greenwald wrote in The Washington Post: "The Trump administration has undoubtedly calculated that Assange's uniquely unpopular status across the political spectrum [in the United States] makes him the ideal test case for creating a precedent that criminalizes the defining attributes of investigative journalism.

"[120] In October 2018, Greenwald said that Bolsonaro was "often depicted wrongly in the Western media as being Brazil's Trump, and he's actually much closer to say Filipino President Duterte or even the Egyptian dictator General el-Sisi in terms of what he believes and what he's probably capable of carrying out.

"[121] Greenwald said that Bolsonaro could be a "good partner" for President Trump "If you think that the U.S. should go back to kind of the Monroe Doctrine as [National Security Adviser] John Bolton talked openly about, and ruling Latin America, and U.S.

Greenwald, who was not detained, called the charges "an obvious attempt to attack a free press in retaliation for the revelations we reported about Minister of Justice Sergio Moro and the Bolsonaro government.

[144] In June 2012, Newsweek magazine named him one of America's Top Ten Opinionists, saying that "a righteous, controlled, and razor-sharp fury runs through a great deal" of his writing, and "His independent persuasion can make him a danger or an asset to both sides of the aisle.

In a February 2014 interview, Greenwald said he risked detention if he reentered the U.S., but insisted that he would "force the issue" on principle, and return for the "many reasons" he had to visit, including if he won a prestigious award of which he was rumoured to be the winner.

[158] Greenwald and Miranda were close friends of Brazilian human rights advocate and politician Marielle Franco, known for criticism of police tactics and corruption, who was fatally shot by unknown assailants.