The second son of a wealthy dealer in priests' robes, he studied the Japanese classics, Confucianism, the doctrines of the Chinese scholar Wang Yang-ming, and also Buddhism and poetics. For a time, he studied with the Buddhist nun and poetess Otagaki Rengetsuni and was influenced by her philosophical attitude toward life. Although he received basic lessons in painting from Osumi Nanko and Ukita Ikkei, he studied painting essentially by himself.

Toward the end of the Edo period, because of his association with supporters of the restoration of Imperial rule, Tomioka came under official displeasure and fled to Nagasaki in 1859. Remaining there even after the Meiji Restoration, he ultimately became a Shintō priest of the Isonokami Shrine (1876) and, later, of the Otori Shrine and made efforts toward their reconstruction. After 1882 he left the priesthood to live a life of painting and scholarly study, becoming a member of the Imperial Fine Arts Academy and the Japan Nanga Society.

Tomioka's paintings, some 20,000 in all, most of which were based on classical Japanese and Chinese literature and legends, are famous for their bold brushstrokes as well as their grand-scale composition. His free-spirited works, either in monochrome or in brilliant colours, convey a strong sense of vitality, with no trace of Western perspective. They won high esteem both at home and abroad, especially after his death, when exhibitions of his paintings were held in the United States, England, France, and other countries. Among his major works are “Gunsen kōkai-zu” (1908; “Hermits Meeting on a Mountain”) and “Abe no Nakamaro meishū bōgetsu-zu” (1908; “The Poet Abe Nakamaro Contemplating the Moon in China”).