Andrew Phillip Cunanan was born on August 31, 1969, the youngest of four children born to US Navy marine, Modesto Cunanan and wife Mary Anne. By the time of his arrival, his parent's marriage had deteriorated to a point where he was raised primarily by his father, due to his mother's chronic depression, caused by the state of her marriage. Although financially comfortable, the young Cunanan sought refuge from the domestic strife, by retreating into the world of adventure novels and comic book fantasies.

These fantasies spilled into his real life and tales of his perfect home life, told to school friends, grew increasingly outlandish, and earned him a reputation as a fantasist.

Following his father's retirement from the Navy, and new found wealth in his job as a stockbroker, Cunanan was sent to a private school in San Diego, where homosexual encounters in his early teens enhanced his already notorious reputation. With his flamboyant, attention-seeking nature well established, he was open about his sexual conquests to other classmates, and earned himself the sobriquet "Most likely not to be forgotten" in the school yearbook. Physically mature for his age, the precocious teen was frequenting the gay bars and clubs of San Diego years ahead of his contemporaries.

After graduation, Cunanan enrolled at the University of California as a history major, but his social life on the gay scene took precedence over everything else. Taking his reinvention fantasies to another level, he developed a myriad of alter egos, realizing that the life of a high-class escort, supported by a steady stream of older gay men, was infinitely preferable to studying or working for a living. Through these relationships with financial high-flyers Cunanan gained access to the highest echelons of San Diego society, developing an expensive taste for all the material gain that this lifestyle offered.

The financial success of Cunanan's father, Modesto, was short-lived, and he was forced to flee to the Philippines following allegations of financial fraud. His mother was forced to sell the family home, to support herself and, around the same time, she became aware of Cunanan's lifestyle. Following a row with his mother, Cunanan decided to drop out of college and follow his father to the Philippines, but he soon missed the perks of his high-flying lifestyle, and returned to the States as soon as he was able, settling in San Francisco, which offered a far more diverse gay culture than that available in San Diego.

Always considered the "gay capital" of the USA, San Francisco provided direct access to Hollywood glamour, and his persuasive way with elder men saw him mingling with the world's superstar elite. It is believed that he met fashion guru Gianni Versace during this time, setting in motion a chain of events that would be the downfall of them both.