The American writer, who was hailed the king of the Beat generation and a hero to many young men, penned The Sea Is My Brother (Penguin) aged 20, based on his years as a merchant seaman.
It features correspondence with his best friend Sebastian Sampas and recalls his "life and experiences" at sea, says the book's editor Dawn Ward.
"This book is really quite important as it shows how Jack developed his writing process," she says.
"The letters that support this period, show that he and Sebastian were reading very important writers and playwrights of the time. They were paying attention to changes in literature styles and autobiographical works."
Ms Ward says the work is especially poignant as he "opens up and shows a side to him that we don't normally see in his books."
The manuscript, which was was discovered in the writer's archive by his brother-in-law, came as a surprise to Kerouac experts, Ms Ward says.
"It was referred to briefly in letters, but nothing that led anyone to believe that there was this really large volume."
Born in 1922, Kerouac began writing from an early age and took to carrying a notebook with him wherever he went, scribbling down notes and penning long, rambling letters to friends and family.
Before writing became his career, the author was a sports reporter, construction worker and joined the Navy twice.
On The Road, about a spontaneous road trip, was and still remains Kerouac's most influential and famous book.
Full story at BBC