Her mother left Jack while pregnant, and Jack refused to acknowledge the baby as his daughter. A blood test when Jan was nine years old proved his paternity and he was ordered to pay $52 a week for her upbringing. Though Jan met her father only twice, she inherited his wanderlust, and like both her parents, Jan made frequent use of drugs and was no stranger to trouble. After a teenage stint in a mental hospital, Jan delved deeper into the 1960s underworld of drugs, before leaving for Mexico at the age of fifteen. For the next few decades, she traveled across the country with a reckless abandon that echoed that of her father and Neal Cassady.
Married and divorced twice, Jan lived a troubled life marked by periods of self-destruction. In 1968, she gave birth to a stillborn child and had no other children.
Jan was an extra in the film Heart Beat, about her father's triangular love affair with Carolyn Cassady and Neal Cassady, and she reportedly gave actor John Heard advice on how to curl his lip like Jack did.
She published two semi-autobiographical novels, Baby Driver in 1981, and Trainsong in 1988. While working on her third novel, Parrot Fever, in Puerto Rico, her kidneys failed, sending her back to the United States. She died in 1996 of kidney disease. At the time of her death, she was involved in legal battles with Stella Sampas Kerouac, Jack's last wife, over his estate, including the location of his grave and ownership of his papers. The battles were ultimately unsuccessful. She is survived by twin half-sisters, Katharine and Sharon, and one half-brother, David.