In 1996, Greenwald founded a law firm concentrating on First Amendment litigation. He began blogging on national security issues in October 2005, when he was becoming increasingly concerned with what he viewed as attacks on civil liberties by the George W. Bush administration in the aftermath of the September 11 attacks.[5][6] He became a vocal critic of the Iraq War and has maintained a critical position of American foreign policy.

Greenwald started contributing to Salon in 2007, and to The Guardian in 2012. 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. His work contributed to The Guardian’s 2014 Pulitzer Prize win and he was among a group of three reporters who won the 2013 George Polk Award. In 2014, he cofounded The Intercept, of which he was an editor until he resigned in October 2020. https://en.m.wikipedia.org/wiki/Glenn_Greenwald

I recommend watching the documentary Citizenfour about Snowden and him.