Greenwald was born on March 6, 1967, in New York City, where he still lives part of the year. He earned a B.A. from George Washington University in 1990 and a J.D. from New York University Law School in 1994. During law school, he worked as an intern and Summer Associate at the New York law firm of Wachtell, Lipton, Rosen & Katz, and after graduation, he practiced law in the Litigation Department at Wachtell, Lipton (1994—1995); in 1996 he co-founded his own litigation firm, called Greenwald Christoph & Holland (later renamed Greenwald Christoph PC), where he litigated cases concerning issues of U.S. constitutional law and civil rights.
One of Greenwald's most notable First Amendment clients was Matthew Hale, a leader of the organization formerly known as the World Church of the Creator and now known as the Creativity Movement, who, on April 6, 2005, was sentenced to a 40-year prison term for soliciting an undercover FBI informant to kill federal judge Joan Lefkow and incarcerated in the United States Penitentiary Administrative Maximum Facility in Florence, Colorado. Although he "represented Hale and his organization in several civil cases" and was not involved in Hale's criminal defense case, after the subsequent killing of Judge Lefkow's mother and husband while Hale was incarcerated for the earlier conviction, Greenwald was enlisted by Hale's mother, Evelyn Hutcheson, to deliver a purportedly "encoded message" from the imprisoned Hale to one of his supporters on the outside; but, despite believing that Hale had been wrongfully convicted and uninvolved in the more recent murders, Greenwald declined to do so.
In his entry in
Unclaimed Territory for July 10, 2006, Greenwald explains, "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."
In the same entry, Greenwald observes that he has been openly gay for 20 years and that, while he has lived in the United States all his life, he divides his time between New York City and Rio de Janeiro, the hometown of his male partner:
Revealingly, American law prevents the recognition of our relationship as a ground for him to live in the United States, while Brazilian law recognizes same-sex relationships for visa and immigration purposes. As a result, for the past year [2006], I have spent substantial time in Brazil while also having a residence in New York. Spending substantial time in another country does not make one an 'expatriate.' And even those American citizens who do give up American residence and live abroad retain full rights of citizenship, including voting rights. But I have not done so.
According to Ken Silverstein's interview with Greenwald published in
Harper's Magazine on February 22, 2008, conducted by telephone while Greenwald was in Brazil, he lives there "much of the time." On July 22, 2008, when Greenwald participated in a debate with Cass Sunstein, an adviser to then Senator Barack Obama, moderated by Amy Goodman on
Democracy Now!, their exchange was also conducted by telephone from Brazil.
In a May, 2008 interview, Greenwald explained that "even though Brazil has the largest Catholic population of any country in the world" and "was a military dictatorship until 1985": "I’m able to obtain from the Brazilian government a permanent visa because my Brazilian partner’s government recognizes our relationship for immigration purposes, while the government of my supposedly 'free,' liberty-loving country enacted a law explicitly barring such recognition."