Glenn Edward Greenwald (born March 6, 1967) is an American journalist, author, and former lawyer.

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. 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. Greenwald subsequently started publishing his own newsletter.

Through The Intercept Brasil in June 2019, Greenwald published leaked conversations between senior officials involved in Operation Car Wash, a corruption case in Brazil. The conversations appeared to show the investigative judge acting prejudicially against Luiz Inácio Lula da Silva in the lead up to the 2018 elections. Greenwald was charged with cybercrimes by Brazilian prosecutors over the leaks in January 2020, though the charges were dismissed by a federal judge a month later. He now hosts the show System Update on Rumble.

Greenwald was born in Queens in New York City to parents Arlene and Daniel Greenwald. Greenwald's family moved to Lauderdale Lakes, Florida, when he was an infant; his parents separated when he was six. Greenwald is Jewish, but grew up without practicing an organized religion, did not have a bar mitzvah, and has said his "moral precepts aren't informed in any way by religious doctrine". Greenwald attended Nova Middle School and Nova High School in Davie, Florida.

Inspired by his grandfather's time on the then-Lauderdale Lakes City Council, Greenwald, still in high school, decided to run at the age of 17 for an at-large seat on the council in the 1985 elections. He was unsuccessful, coming in fourth place with 7% of the total vote. In 1991, Greenwald ran again, coming in third place with 18% of the vote. After that, he stopped running for political office and instead focused on law school.

He received a B.A. in philosophy from George Washington University in 1990 and a J.D. from New York University School of Law in 1994. His experiences on his college debate team influenced his career path. "That developed, I think, a lot of the skills and interest that ended up guiding my future career," he said in an interview.

Greenwald practiced law in the litigation department at Wachtell, Lipton, Rosen & Katz from 1994 to 1995. In 1996, he co-founded his own litigation firm, Greenwald Christoph & Holland (later renamed Greenwald Christoph PC), where he litigated cases concerning issues of U.S. constitutional law and civil rights. 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, and the neo-Nazi National Alliance.