Joseph Lyle Menendez was born on January 10, 1968, in New York City. He was the elder son of José Menendez, a Cuban immigrant and successful entertainment executive, and Mary Louise "Kitty" Menendez, a former schoolteacher. The family later moved to Princeton, New Jersey, where Lyle and his younger brother, Erik, were raised in an affluent environment.

Lyle attended Princeton Day School and later enrolled at Princeton University but was suspended for plagiarism. He transferred to the University of California, Irvine, but did not complete his degree. The brothers were known for their lavish lifestyle, funded by their parents' wealth.

On August 20, 1989, Lyle and Erik Menendez murdered their parents, José and Kitty Menendez, in their Beverly Hills home. Armed with 12-gauge shotguns, they shot their father in the back of the head and their mother multiple times, leaving her unrecognizable. The brothers then attempted to make the scene appear as a mob hit and established alibis by attending a movie and disposing of the weapons.

Initially, the brothers were not suspects, but their extravagant spending following the murders raised suspicions. In March 1990, Erik confessed to his psychologist, who reported it to the police, leading to their arrests.

The first trials in 1993 ended in mistrials. In 1996, a retrial convicted both brothers of first-degree murder, and they were sentenced to life imprisonment without the possibility of parole.

In May 2025, a Los Angeles judge resentenced Lyle and Erik Menendez to 50 years to life, making them eligible for parole. The decision considered new evidence and the brothers' behavior during incarceration.