In 1968, Steinbeck returned to Vietnam as a journalist. Along with Sean Flynn, son of actor Errol Flynn, he started Dispatch News Service, which originally published the story on the My Lai Massacre by Seymour Hersh. Fluent in street Vietnamese, Flynn and Steinbeck quickly became independent of the flow of information dispensed by the United States Press Office. Hence, they were the first to disclose the truth about the My Lai Massacre and the Con Son Island prison "tiger cages". Flynn disappeared in Cambodia on a photo shoot.

Steinbeck's Vietnam memoir In Touch was published by Knopf in 1969. He wrote about his experiences with the Vietnamese, the GIs and his interlude with that culture. Steinbeck took the vows of a Buddhist monk while living on Phoenix Island in the middle of the Mekong Delta, under the tutelage of the politically powerful Coconut Monk, a silent tree-dwelling Buddhist yogi who adopted Steinbeck as a spiritual son. Steinbeck stayed in the "peace zone" created by the monk in the midst of the raging war, where howitzer shells were hammered into bells by the 400 monks who lived on the island.

Steinbeck traveled back and forth between Asia and the United States several more times before settling in Boulder, Colorado where he studied Tibetan Buddhism with Chögyam Trungpa. On March 6, 1982, he married Nancy Harper, who had two children from a previous marriage. Steinbeck already had one child when they met. In 1983, the family traveled around the world for a year, living in Kathmandu in order to further their Buddhist studies. Although John and Nancy divorced in 1989 due to his alcoholism, they continued to live together until the day he died.

In 1984, Steinbeck was diagnosed with hemochromatosis, a genetic disease that causes iron retention in the organs. Steinbeck got sober in 1988 after years of heavy drinking. He became very interested in the genetic aspects of alcoholism, and was a participant in 12 Step programs.

It was Steinbeck who broke the story of Ösel Tendzin's AIDS to the Boulder press. Subsequently he renewed his journalistic career, writing articles about their travels with the Dalai Lama, Tibetan Buddhism, alcoholism and the toll it takes on loved ones. In 1990, he began his autobiography with this statement:

"The reasons for attempting to write this book could be summed up simply by my desire to live free from fear. However, the path leading to that sort of fruition has, along its border, a lot of fearful things that at first glance can cause panic, or resentment, or shame. There is also charity and sanity, which accompany this sort of voyage like good dolphins on a good quest. Frankly, I feel blessed that these guiding elements have never abandoned me and, as I and others continue to recover from the effects of my actions, I am encouraged that these qualities will endure, even shine."

In 1990, Steinbeck was diagnosed with a ruptured disc. He underwent corrective surgery on February 7, 1991, and died immediately after the operation. In 2001, his posthumous memoir, The Other Side of Eden was published by Prometheus Books. The book jacket states "Left unfinished at his untimely death, this testament to his life is here reconstructed by Nancy Steinbeck. Interweaving her own reminiscences of her life with John Steinbeck IV, Nancy has created an engrossing account from two perspectives: John's memories of his chaotic and adventurous upbringing and her own thoughts on their journey together to make a new life apart from the long shadow of a famous father and a troubled past." The book is co-distributed by Hazelden, America's foremost treatment center for drug and alcohol addiction.

Publisher's Weekly said "More than a memoir, this is a powerful account of healing and liberation. This book can help many people."