Lamo was born in Boston, Massachusetts to Mario Lamo and Mary Lamo-Atwood in 1981. He spent his early childhood in Arlington, Virginia, until moving to Bogotá, Colombia around the age of 10. When his family moved back to the United States two years later, they settled in San Francisco, where Adrian lived until he tested out of High School a year early. Popularly called the "homeless hacker" for his transient lifestyle, Lamo spent most of his travels couch-surfing, squatting in abandoned buildings and traveling to Internet cafes, libraries and universities to investigate networks, and sometimes exploiting security holes. Despite performing authorized and unauthorized vulnerability assessments for several large, high-profile entities, Lamo refused to accept payment for his services. During this period he also overdosed on amphetamines.

Lamo was appointed to the Lesbian, Gay, Bisexual, Transgender, Queer and Questioning Youth Task Force by San Francisco Supervisor Tom Ammiano.

In a 2004 interview with Wired, an ex-girlfriend of Lamo's described him as "very controlling," stating: "He carried a stun gun, which he used on me." According to the same article, a court issued a restraining order against Lamo. Lamo disputed the accuracy of the article and wrote "I have never been subject to a restraining order in my life".

In February 2009 Lamo was revealed to have been a donor to disclosure site Wikileaks.

In his spare time, he donates his time and expertise to Voluntary Legal Services of Northern California, a Sacramento-based nonprofit organization providing assistance to indigent and low-income clients involved in civil litigation.[citation needed]

In May 2010 at age 29, he was diagnosed with Asperger's syndrome after having been placed on a 72-hour involuntary psychiatric hold, which was extended to a total of nine days.

Adrian Lamo is perhaps best known for breaking into The New York Times internal computer network in February 2002, adding his name to confidential databases of expert sources, and using the paper's LexisNexis account to conduct research on high-profile subjects, although his first published activities involved operating AOL watchdog site Inside-AOL.com. The Times filed a complaint and a warrant for Lamo's arrest was issued in August 2003 following a 15 month investigation by federal prosecutors in New York. At 10:15 AM on September 9, after spending a few days in hiding, he surrendered to the US Marshals in Sacramento, California. He re-surrendered to the FBI in New York City on September 11, and pled guilty to one count of computer crimes against Microsoft, Lexis-Nexis and The New York Times on January 8, 2004.

Later in 2004, Lamo was sentenced to six months detention at his parents' home plus two years probation, and was ordered to pay roughly $65,000 in restitution. He was convicted of compromising security at The New York Times and Microsoft, Yahoo! and MCI WorldCom.

When challenged for a response to allegations that he was glamorizing crime for the sake of publicity, his response was "Anything I could say about my person or my actions would only cheapen what they have to say for themselves." When approached for comment during his criminal case, Lamo frustrated reporters with non sequiturs such as "Faith manages", (probably a reference to science fiction television show Babylon 5) and "It's a beautiful day."

At his sentencing, Lamo expressed remorse for harm he had caused through his intrusions, with the court record quoting him as adding "I want to answer for what I have done and do better with my life."