Lucien Carr was born on March 1, 1925, in New York City. His parents were Marion Howland and Russell Carr, both from well-known families in St. Louis, Missouri. His maternal grandfather, Benjamin Gratz, was a businessman engaged in the rope-making industry and was part of Philadelphia's early Jewish community. In 1930, when Lucien was five years old, his parents separated. After the separation, Lucien and his mother moved back to St. Louis, where he spent most of his childhood.

At the age of 12, Carr met David Kammerer, who became a significant figure in his life. Kammerer was a teacher at Washington University in St. Louis and had connections with prominent families in the area. He had been friends with William S. Burroughs, who was also affluent and knew the Carr family. Kammerer met Carr while leading a Boy Scout troop that Carr was a member of. He quickly developed a strong fascination with Carr.

Over the next five years, Kammerer pursued Carr, showing up frequently at the schools he attended. Carr and those close to him claimed that Kammerer's attention was relentless and invasive. This led to Carr moving from school to school, attending Phillips Academy in Massachusetts, Bowdoin College in Maine, and the University of Chicago. Kammerer followed him to each institution and occasionally socialized with him. However, Carr maintained that he never had a sexual relationship with Kammerer.

Carr's time at the University of Chicago ended abruptly after he tried to harm himself by putting his head in a gas oven. He described the incident as a "work of art," but his family believed it was a suicide attempt related to Kammerer's pursuit of him. This led to Carr spending two weeks in a psychiatric hospital. Afterwards, his mother brought him to New York City and enrolled him at Columbia University.

Despite his mother's efforts to keep him away from Kammerer, he followed Carr to New York, moving into an apartment near Carr. At Columbia, Carr was recognized as an intelligent and engaging student. He became involved in campus activities and formed friendships with other notable figures of the Beat Generation like Allen Ginsberg and Jack Kerouac. 

On August 13, 1944, Lucien Carr and Jack Kerouac tried to leave New York City on a merchant ship to France, fulfilling a fantasy of traveling together. They were not able to board the ship, so they spent time at the West End Bar, where they drank. Kerouac left and soon encountered David Kammerer, who was looking for Carr. Kammerer found Carr at the bar, and the two men went for a walk that ended in Riverside Park.

According to Carr, he and Kammerer were resting when Kammerer made another sexual advance. Carr claimed he rejected Kammerer, who then physically assaulted him. In a panic, Carr said he took out his Boy Scout knife and stabbed Kammerer. After the struggle, Carr tied Kammerer's hands and feet and weighted the body with rocks before dumping it into the Hudson River.

Following the act, Carr went to the apartment of William Burroughs. He handed Burroughs Kammerer's bloodied pack of cigarettes and described what happened. Burroughs advised Carr to find a lawyer and turn himself in, but instead, Carr sought out Kerouac. With Kerouac's assistance and that of Abe Green, they disposed of the murder weapon and some belongings of Kammerer. They then went to see a movie and visit the Museum of Modern Art.

Carr later went to his mother's house and then turned himself in at the office of the New York District Attorney, where he confessed to the crime. The authorities kept him in custody while they located Kammerer's body. Carr pointed out where he had hidden Kammerer's eyeglasses in Morningside Park.

Charges of second-degree murder followed. The media coverage was intense due to Carr's reputation as a gifted student and the dramatic elements surrounding the case, including themes of homosexuality and self-defense. Carr ultimately pleaded guilty to first-degree manslaughter. His mother testified about Kammerer's behavior, and he received a prison sentence of one to twenty years. He served two years in Elmira Correctional Facility and was released.