Andrew Phillip Cunanan was born August 31, 1969 in National City, California, to Modesto "Pete" Cunanan, a Filipino American, and Mary Anne Schillaci, an Italian American, the youngest of four children. Modesto was serving in the US Navy in the Vietnam War at the time of his son's birth; after leaving the Navy, where he had served as a career officer, he worked as a stockbroker.

In 1981, Cunanan's father enrolled him in the independent day school, The Bishop's School in the affluent La Jolla neighborhood of San Diego. At school, Cunanan was remembered as being bright and very talkative, and testing with an I.Q. of 147. As a teenager, however, he developed a reputation as a prolific liar given to telling fantastic tales about his family and personal life. He was also adept at changing his appearance according to what he felt was most attractive at a given moment. Nonetheless, in high school he was voted Least Likely to be Forgotten.

After graduating from high school in 1987, Cunanan enrolled at the University of California, San Diego, where he majored in American History. After dropping out, two years later, he settled in the Castro District of San Francisco.

In 1988, when Cunanan was 19, Modesto deserted his family and moved to the Philippines, to avoid arrest for embezzlement. That same year, Cunanan - who was openly gay in high school and even then had liaisons with wealthy older men - had begun frequenting local gay clubs and restaurants, and his deeply religious mother Mary Anne learned that Cunanan was gay.

In 1990, Cunanan met Gianni Versace at Colossus, a San Francisco nightclub. Versace was in town to be feted for the costumes he had designed for the opera Capriccio.

In 1996, Cunanan and Norman Blachford, the wealthy older man who had been hosting and financially supporting him, broke up. Cunanan, now on his own, maxed out his credit cards. Cunanan's friend, Jeffrey "Jeff" Trail, had told Trail's former roommate, Michael Williams, that Cunanan had resumed his old profession: selling drugs. Cunanan also began increasingly consuming them.

On July 23, 1997, eight days after killing Versace, Cunanan killed himself with a self-inflicted gunshot through the mouth, in the upstairs bedroom of a Miami Beach houseboat. He used the same gun he had used to kill Madson, Reese, and Versace: a Taurus PT100 semi-automatic pistol in .40 S&W caliber, which he had stolen from the first victim, Jeff Trail. Cunanan's cremated remains are interred in the mausoleum at Holy Cross Catholic Cemetery in San Diego, California.

Cunanan is portrayed by Shane Perdue in the film The Versace Murder (1998), and by Luke Morrison in the television film House of Versace (2013).

Indiana, Gary. Three Month Fever: The Andrew Cunanan Story. Cliff Street/HarperCollins. 

The American rock band Modest Mouse's album Strangers to Ourselves (2015) includes a song named after the case: "Pistol (A. Cunanan, Miami, FL. 1996)".

Cunanan is portrayed by Darren Criss in The Assassination of Gianni Versace: American Crime Story, the second season of the anthology series American Crime Story, which premiered on January 17, 2018.