Gonzo journalism is a style of journalism that is written without claims of objectivity, often including the reporter as part of the story using a first-person narrative. The word "gonzo" is believed to have been first used in 1970 to describe an article about the Kentucky Derby by Hunter S. Thompson, who popularized the style. It is an energetic first-person participatory writing style in which the author is a protagonist, and it draws its power from a combination of social critique and self-satire. It has since been applied to other subjective artistic endeavors.

Gonzo journalism involves an approach to accuracy that concerns the reporting of personal experiences and emotions, in contrast to traditional journalism, which favors a detached style and relies on facts or quotations that can be verified by third parties. Gonzo journalism disregards the strictly edited product once favored by newspaper media and strives for a more personal approach; the personality of a piece is as important as the event or actual subject of the piece. Use of sarcasm, humour, exaggeration, and profanity is common.

Thompson, who was among the forefathers of the New Journalism movement, said in the February 15, 1973, issue of Rolling Stone, "If I'd written the truth I knew for the past ten years, about 600 people—including me—would be rotting in prison cells from Rio to Seattle today. Absolute truth is a very rare and dangerous commodity in the context of professional journalism."

The term gonzo was first used in connection with Hunter S. Thompson by The Boston Globe magazine editor Bill Cardoso in 1970. He described Thompson's article "The Kentucky Derby Is Decadent and Depraved", which was written for the June 1970 edition of Scanlan's Monthly, as "pure Gonzo journalism". This predates the December 1970 debut of the Muppet Gonzo in The Great Santa Claus Switch. Cardoso said gonzo was South Boston Irish slang describing the last man standing after an all-night drinking marathon. He also said it was a corruption of the Canadian French word gonzeaux, which means 'shining path', although this is disputed.

Another speculation is that the word may have been inspired by the 1960 hit song "Gonzo" by the rhythm and blues pianist James Booker. This possibility is supported by a 2007 oral biography of Thompson, which states that the term is taken from a song by Booker but does not explain why Thompson or Cardoso would have chosen the term to describe Thompson's journalism. The 2013 documentary Bayou Maharaja: The Tragic Genius of James Booker quotes Thompson's literary executor as saying that the song was the origin of the term. According to a Greg Johnson biographical note on Booker, the song title "Gonzo" comes from a character in a movie called The Pusher, which in turn may have been inspired by a 1956 Evan Hunter novel of the same title.

In 2025, David S. Wills, author of High White Notes: The Rise and Fall of Gonzo Journalism, investigated the origins of the word "gonzo" and discovered that Cardoso had found it in an article he had edited for The Boston Globe Sunday Magazine just a week prior to calling Thompson's story "pure Gonzo journalism." The article was about countercultural icon Baba Ram Dass and "gonzo" was used "with the context suggesting 'going wild' or 'losing control' on a hallucinogenic substance." The original article said that Dass "smoked pot and went gonzo on STP, the most powerful hallucinogenic ever concocted."

Thompson based his style on William Faulkner's notion that "fiction is often the best fact". While the things that Thompson wrote about are basically true, he used satirical devices to drive his points home. He often wrote about recreational drugs and alcohol use, which added subjective flair to his reporting. The term "gonzo" has also come into (sometimes pejorative) use to describe journalism in Thompson's style, characterized by a drug-fueled stream of consciousness writing technique.

Fear and Loathing in Las Vegas followed the Mint 400 piece in 1971 and included a main character by the name of Raoul Duke, accompanied by his attorney, Dr. Gonzo, with defining art by Ralph Steadman. Although this book is considered a prime example of gonzo journalism, Thompson regarded it as a failed experiment. He had intended it to be an unedited record of everything he did as it happened, but he edited the book five times before publication.