Onosato Toshinobu was born in Iida City, Nagano Prefecture where he lived until moving to Kiryu City in Gumma Prefecture in 1922. He studied painting with Tsuda Seifu (1880-1978), a reknowned western-style painter. In 1935 he exhibited with the Nika artists' association in Tokyo and was a member of the Jiyu association from 1938-56. Having served in Manchuria from 1941-45, he was a prisoner-of-war in Siberia from 1945-48.

Onosato won the Grand Prize at the Tokyo Biennial in 1963. His exhibition record includes one-man shows in Tokyo at the Takemiya Gallery in 1953, the Mimatsu Gallery in 1955, the Kabutoya Gallery in Tokyo in 1958, The Gress Gallery in Washington, D.C. 1960-61, the Minami Gallery in Tokyo in 1962, the Homma Museum of Art in Sakata City in 1971, the Kornfeld Gallery in Zurich in 1972, the Soker-Kaseman Gallery in San Francisco in 1980, Mikimoto Hall in Tokyo in 1980 and the Onosato Association in Katsuyama City in 1981.

Among important group exhibitions are the National Museum of Modern Art, Tokyo in 1964 and 1982, the Venice Biennial in 1964 and 1966, the Guggenheim Museum in 1964, the Kunsthaus in Zurich in 1965, the Louisana Museum in Copenhagen in 1974, Tokyo Central Museum in 1977 and 1983, the Museum of Modern Art in Tokyo and Toyama City in 1982, and in 1983 at the Gumma Prefectural Museum and the Tokyo Metropolitan Museum.

Onosato's work is in the collections of the Museum of Contemporary Art in Nagaoka, and the National Museum of Modern Art in Tokyo, among numerous others.