Joshu Sasaki became an ordained monk at age thirteen under his teacher, Joten Soko Miura. Soon after, he followed Joten Soko Miura to Myoshin-ji, the head temple of one of the largest branches of Rinzai. Having been awarded the title of roshi in 1947, Kyozan Joshu Sasaki took the position of an abbot at Yotoku-in. In 1953 he was appointed abbot of Shojuan.
In 1962, at the request of Daiko Furukawa, Joshu decided to travel to the United States to teach students in the West, founding a Zen center in Los Angeles.
Joshu Sasaki regularly offered formal training sessions at both the Mount Baldy Zen Center and the Bodhi Manda Zen Center, occasionally offering sesshin at the Rinzai-Ji Zen Center in Los Angeles and Haku-un-ji Zen Center in Tempe, Arizona, as well as at numerous other centers on the American East Coast, and in Europe. Roshi's teaching schedule greatly depended on his health, however. In early February 2012 Joshu Roshi became ill with aspiration pneumonia and did not teach at MBZC (or any affiliate Zen Center) again. On November 10, at a dedication ceremony for the Zendo remodel, Joshu Roshi officially resigned as abbot of the Mount Baldy Zen Center for health reasons.
Joshu Sasaki has given full Rinzai priest ordination to approximately 20 students, which grants them the title oshō. But Kyozan Joshu Sasaki did not give dharma transmission, which is in Rinzai the qualification needed to train students in a trainghall to become a priest. Nevertheless, several of his students are recognized by their community "as wise guides of various communities".
One of his best known students is Canadian poet and singer-songwriter Leonard Cohen, who served as personal assistant to Joshu Sasaki during his 1990s seclusion to the Mt. Baldy monastery. Many of the poems in Cohen's 2006 Book of Longing refer to Mt. Baldy and Joshu Sasaki (mostly referred to as "Roshi").
In a 24 December 2009 interview Eshin Godfrey, Abbot of the Zen Centre of Vancouver and a student of Sasaki-roshi, said of his teacher,
He has become a precious golden Buddha! You can only have great gratitude for your teacher, even though I've found it a bitter-sweet relationship. As the western styles of Zen develop I'm grateful to have started study in the traditional way.
Joshu Sasaki died at Cedars Sinai Hospital in Los Angeles on July 27, 2014, aged 107.
As early as 1997, it was put forth by members of his Mt. Baldy Zen Center that Sasaki Roshi was engaging in sexual misconduct with his female students. Sasaki was 90 years old at that point. The issue was not resolved at that time. Part of a letter written by the monks, nuns, and students of Mt. Baldy Zen Center reads as follows:
With sadness and confusion we have struggled with your sexual behavior toward women. In the past open discussion was discouraged, and people were left feeling afraid to raise their concerns about this matter. But this fall we have been meeting to air our concerns and to try to come to a better understanding of the problem.
Awareness of Joshu Roshi's sexual misconduct existed since the early 1970s. Stephen Wilder trained at Mt. Baldy from 1974-75 and was ordained as a monk in 1977. During that time he had heard rumors of Joshu Roshi's sexual misconduct. Finally, in January 1982 he resigned because he could no longer tolerate the duplicity. He writes:
It wasn't until his Inji, who was engaged to be married, came bursting into my room at Bodhi Mandala in New Mexico after lunch one day during an autumn sesshin, sobbing and saying, "He won't leave me alone", that it finally dawned on me that this was real. Until then I truly did not believe any of the rumors because of my own conditioned ignorance.
A student of Joshu Roshi, Giko David Rubin, raised concerns about Roshi's sexual conduct to Joshu Roshi himself as well as his inner circle, and this was part of the response:
Joshu Roshi told me I would never get enlightened if I thought about these things. I was told by one Osho and one senior student I would be blamed for Joshu Roshi's death if I tried to make him change his behavior, and that I would be responsible for ruining his legacy. "You are killing him!" was shouted at me more than once.
In 2012, Eshu Martin, a former monk in Rinzai-ji and student of Sasaki, also publicly accused Sasaki, who was then 105 years old, of sexual misconduct with his students.
His career of misconduct has run the gamut from frequent and repeated non-consensual groping of female students during interview, to sexually coercive after hours "tea" meetings, to affairs and sexual interference in the marriages and relationships of his students.
A February 2013 article in the Albuquerque Journal stated:
In early January, the senior teachers of Sasaki's community admitted in an on-line statement that the community "has struggled with our teacher Joshu Sasaki Roshi's sexual misconduct for a significant portion of his career in the United States."