Eugene Louis Vidal was born in the cadet hospital of the U.S. Military Academy at West Point, New York, the only child of Eugene Luther Vidal (1895-1969) and Nina S. Gore (1903-1978). Vidal was born at the West Point cadet hospital because his first lieutenant father was the first aeronautics instructor of the military academy. The middle name, Louis, was a mistake on the part of his father, "who could not remember, for certain, whether his own name was Eugene Louis or Eugene Luther". In the memoir Palimpsest (1995), Vidal said, "My birth certificate says 'Eugene Louis Vidal': this was changed to Eugene Luther Vidal Jr.; then Gore was added at my christening [in 1939]; then, at fourteen, I got rid of the first two names."

In the multi-volume memoir The Diary of Anais Nin (1931-74), Anais Nin said she had a love affair with Vidal, who denied her claim in his memoir Palimpsest (1995). Vidal also said that he had an intermittent romance with the actress Diana Lynn, and alluded to possibly having fathered a daughter. Yet, regarding Nin, in the online article "Gore Vidal's Secret, Unpublished Love Letter to Anais Nin" (2013), author Kim Krizan said she found an unpublished love letter from Vidal to Nin, which contradicts his denial of a love affair with Nin. Krizan said she found the love letter while researching Mirages, the latest volume of Nin's uncensored diary, to which Krizan wrote the foreword. Moreover, he was briefly engaged to the actress Joanne Woodward before she married the actor Paul Newman; after marrying, they briefly shared a house with Vidal in Los Angeles.  In 1950, Gore Vidal met Howard Austen, who became his partner for the next 53 years. He said that the secret to his long relationship with Austen was that they did not have sex with each other, "It's easy to sustain a relationship when sex plays no part, and impossible, I have observed, when it does." In Celebrity: The Advocate Interviews (1995), by Judy Wiedner, Vidal said that he refused to call himself "gay" because he was not an adjective, adding "to be categorized is, simply, to be enslaved. Watch out. I have never thought of myself as a victim... . I've said - a thousand times? - in print and on TV, that everyone is bisexual".  In an interview with Esquire in 1969, Gore said "Homosexuality is as natural as heterosexuality. Notice I use the word natural, not normal." Commenting his life's work and his life, he described his style as "Knowing who you are, what you want to say, and not giving a damn."  In the course of his life, Vidal lived at various times in Italy and in the United States. In 2003, as his health began to fail with age, he sold his Italian villa La Rondinaia (The Swallow's Nest) on the Amalfi Coast in the province of Salerno and he and Austen returned to Los Angeles. Howard Austen died in November 2003 and in February 2005 his mortal remains were re-buried at Rock Creek Cemetery, in Washington, D.C., in a joint grave plot that Vidal had purchased for himself and Austen.

How did he refer to his sexuality?
I have never thought of myself as a victim... . I've said - a thousand times? - in print and on TV, that everyone is bisexual".