Carr was born in New York City; his parents, Russell Carr and Marian Gratz Carr, were both products of socially prominent St. Louis families. After his parents separated in 1930, young Lucien and his mother moved back to St. Louis; Carr spent the rest of his childhood there.

At the age of 14, Carr met David Kammerer (b. 1911), a man who would have a profound influence on the course of his life. Kammerer was a teacher of English and a physical education instructor at Washington University in St. Louis. Kammerer was a childhood friend of William S. Burroughs, another scion of St. Louis wealth who knew the Carr family. Burroughs and Kammerer had gone to primary school together, and as young men, they traveled together and explored Paris’s night life: Burroughs said Kammerer “was always very funny, the veritable life of the party, and completely without any middle-class morality.” Kammerer met Carr when he was leading a youth group of which Carr was a member, and quickly became infatuated with the teenager.

Over the next five years, Kammerer pursued Carr, showing up wherever the young man was enrolled at school. Carr would later insist, as would his friends and family, that Kammerer had been hounding Carr sexually with a predatory persistence that would today be considered stalking. Whether Kammerer’s attentions were frightening or flattering to the younger man (or both) is now a matter of some debate among those who chronicle the history of the Beat Generation. What is not in dispute is that Carr moved quickly from school to school: from the Phillips Academy in Andover, Massachusetts to Bowdoin College in Brunswick, Maine to the University of Chicago, and that Kammerer followed him to each one. The two of them socialized on occasion. Carr always insisted, and Burroughs believed, that he never had sex with Kammerer; Jack Kerouac biographer Dennis McNally wrote that Kammerer "was a Doppelgänger whose sexual desires Lucien would not gratify; their connection was an intertwined mass of frustration that hinted ominously of trouble."

Carr’s University of Chicago career ended quickly and badly, with an episode that concluded with the young man putting his head into a gas oven. He explained away this act as a “work of art,” but the apparent suicide attempt, which Carr’s family believed was catalyzed by Kammerer, led to a two-week stay in the psychiatric ward at Cook County hospital. Carr’s mother, who had by this time moved to New York City, brought her son there and enrolled him at Columbia University, close to her own home.

If Marian Carr was seeking to protect her son from David Kammerer, she did not succeed. Kammerer soon quit his job and followed Carr to New York, moving into an apartment on Morton street in the West Village.

William Burroughs also moved to New York, to an apartment a block away from Kammerer. The two older men remained friends.

As a freshman at Columbia, Carr was recognized as an exceptional student with a quick, roving mind. A fellow student from Lionel Trilling’s humanities class described him as “stunningly brilliant…. It seemed as if he and Trilling were having a private conversation.”

It was also at Columbia that Carr befriended Allen Ginsberg in the Union Theological Seminary dormitory on 122nd street (an overflow residence for Columbia), when Ginsberg knocked on the door to find out who was playing a recording of a Brahms trio. Soon after, a young woman Carr had befriended, Edie Parker, introduced Carr to her boyfriend, Jack Kerouac, then twenty-two and nearing the end of his short career as a sailor. Carr, in turn, introduced Ginsberg and Kerouac to one another – and both of them to his older friend with more first-hand experience at decadence: William Burroughs. The core of the New York Beat scene had formed, with Carr at the center. As Ginsberg put it, “Lou was the glue.”

Carr, Kerouac, Ginsberg and Burroughs explored New York’s grimier underbelly together. Carr had a taste for provocative behavior, for bawdy songs and for coarse antics aimed at shocking those with staid middle-class values. According to Kerouac, Carr once convinced him to get into an empty beer keg, which Carr then rolled down Broadway. Ginsberg wrote in his journal at the time: “Know these words, and you speak the Carr language: fruit, phallus, clitoris, cacoethes, feces, foetus, womb, Rimbaud.” It was Carr who first introduced Ginsberg to the poetry and the story of Arthur Rimbaud, the 19th-century French poet whose youthful brilliance, decadent style and early death make him an enduring favorite among college students. Rimbaud would be a major influence on Ginsberg’s poetry.

Ginsberg was plainly fascinated by Carr, whom he viewed as a self-destructive egotist but also as a possessor of real genius. Fellow students saw Carr as talented and dissolute, a prank-loving late-night reveler who haunted the dark pockets of Chelsea and Greenwich Village until dawn, without making a dent in his brilliant performance in the classroom. On one occasion, asked why he was carrying a jar of jam across the campus, Carr simply explained that he was “going on a date.” Returning to his dorm in the early hours another morning to find that his bed had been short-sheeted, Carr retaliated by spraying the rooms of his dorm-mates with the hallway fire-hose – while they were still sleeping.