Born in Shiga district, Ōmi (Ōtsu, Shiga), son of Mitsu no Obito Momoe of an immigrant family (some say 766). His childhood name was Hirono.
Around this time he entered the Ōmi provincial temple to study under the monk Gyōhyō, and two years later was tonsured, taking the name Saichō.
He received full ordination at Tōdai-ji in Nara. Instead of pursuing a career, he built a small hermitage on Mount Hiei near his home and began solitary practice.
He built the Ichijō Shikan-in (later the main hall of Enryaku-ji) on Mount Hiei, enshrining the healing Buddha. The "eternal flame" said to have been lit then is still kept burning today.
He was chosen as one of the ten court chaplains, and later won the deep trust of Emperor Kanmu.
He went to Tang China with the embassy as a short-term scholar. In the same fleet was Kūkai, future founder of Shingon. At Mount Tiantai he studied the Tiantai teachings.
Having learned Zen and esoteric Buddhism as well as Tiantai, he returned after about a year with many scriptures, and prayed for the ailing Emperor Kanmu.
The court allowed Tendai to ordain two monks each year, regarded as the founding of the Tendai school.
He received an esoteric consecration from the younger Kūkai and borrowed scriptures to study. But his disciple Taihan left for Kūkai, and they disagreed over lending texts, so the two gradually drifted apart.
Touring the east to spread the teachings, he engaged in a long debate with the Aizu monk Tokuitsu on whether all beings can become buddhas.
He wrote the Sange Gakushō Shiki on training monks: "One who lights up a corner is a national treasure." He petitioned for an ordination platform on Mount Hiei, but the Nara temples strongly objected.
He died on Mount Hiei at 55. Seven days later the court approved the Mahayana ordination platform he had long sought. He was later honored as Dengyō Daishi, and Enryaku-ji became the "mother mountain" that trained Hōnen, Shinran, Nichiren and others.
Sakanoue no TamuramaroKūkaiSugawara no MichizaneSei ShōnagonFujiwara no MichinagaMurasaki ShikibuFujiwara no YorimichiTaira no Kiyomori
People of the Heian period ・ People by period
Based on facts found in textbooks and biographies. Uncertain points are marked as such.