Stompanato is interred at Oakland Cemetery, in Woodstock, McHenry County, Illinois beside his mother Carmela (1890–1925), his father John (1890–1952), and his stepmother Verena (1901–1967). His brother Carmine (1912–1961) is buried nearby.

John Stompanato Jr., was born into an Italian American family in Woodstock, Illinois. His father, John Sr., owned a barber shop and his mother, Carmela, was a seamstress. Both parents were born in Italy but were married in Brooklyn. They had moved to Woodstock in 1916. Stompanato was the youngest of four children: he had two older sisters, Grace and Teresa; and an older brother, Carmine. Six days after his birth, his mother died of peritonitis. Johnny's father soon married a woman named Verena Freitag.

In 1940, after Stompanato's freshman year at Woodstock High School, his father sent him to Kemper Military School for boys in Boonville, Missouri. In 1942, he graduated at the age of 17. In 1943, Stompanato joined the U.S. Marines serving with the 1st Service Battalion, 1st Marine Division. He served in the South Pacific theater, in Peleliu and Okinawa, and then served in China. Stompanato left the Corps in March 1946, being discharged in China.

Stompanato met his first wife, Sarah Utish, a Turkish woman, while stationed in Tianjin, China. Stompanato converted to Islam in order to marry her in May 1946. They returned to Woodstock, where they had their first son, John Stompanato III. During this time, Stompanato worked as a bread salesman. However, after his wife walked out on him (she would later remarry and live in Hammond, Illinois), he moved to Hollywood, California in 1947.

After moving to Los Angeles, Stompanato owned and managed "The Myrtlewood Gift Shop" in Westwood. The Business sold inexpensive pieces of crude pottery and wood carvings as fine art. Through connections to the LA underworld, he became a bodyguard for gangster Mickey Cohen and as well as an enforcer for his crime family. Stompanato also established himself within Hollywood society. In 1948, Frank Sinatra asked Cohen to tell Stompanato to keep away from Ava Gardner. But the mob boss instead told Sinatra to go back to his wife and children, because he never got between men and their “broads.” In the same year, Stompanato married for a second time, to 33-year-old Actress Helen Gilbert. In August 1949, Stompanato testified at a coroner's inquest into the shotgun slaying of Edward "Neddy" Herbert, an associate of Cohen. Within a year, Gilbert had filed for divorce. She said of Stompanato "[he] had no means. I did what I could to support him.”

In the mid-1950s, he began an abusive relationship with Actress Lana Turner. In 1958, he was stabbed to death by Turner's daughter, Cheryl Crane, who said she did it to defend her mother from a vicious beating by Stompanato. His death was ruled as justifiable homicide because he had been killed in self-defense.

In October 1952, Stompanato left Cohen and started dating Helene Stanley, a former 20th Century Fox contract player. By December, he was working as her manager. The following year, she became his third wife; however, they divorced two years later. Throughout the 1950s, he was arrested seven times by the LAPD for various Criminal charges ranging from vagrancy to suspicion of robbery.

Their relationship was stormy; it was often punctuated with frequent arguments and fights. In 1957, Stompanato became so jealous about Turner's relationship with Future James Bond actor Sean Connery, he flew to the United Kingdom. He stormed onto the set of Another Time, Another Place threatening Connery with a gun. Unperturbed, the 6 ft 2 in Scotsman, who was a former body builder and karate black belt, bent Stompanato's hand back forcing him to drop the weapon. He was reported to the police and quietly deported from the United Kingdom. After Stompanato's death, it was rumored that at least one LA mobster held Connery responsible, leading the actor to go into hiding for a short time afterwards.

On April 4, 1958, Stompanato was stabbed to death by Turner's teenage daughter Cheryl Crane at her mother's home in Beverly Hills, California. She claimed that Stompanato had been violently attacking her mother, so she stabbed him. A coroner's inquest returned a decision of justifiable homicide. After the ruling, Stompanato's family sued Turner for $750,000 (later settled for $20,000).