Born in Okayama, Japan, in 1938, Mieko Shiomi studied music at the Tokyo University of the Arts. She became a central figure in the Japanese avant-garde scene during the 1960s, eventually joining the international Fluxus network after relocating to New York in 1964.

Shiomi is recognized for her development of Spatial Poems, a series of mail-art projects that invited participants worldwide to perform simple, conceptual actions. Her practice frequently bridges the gap between musical composition and performance art, utilizing text-based scores that emphasize temporal and spatial awareness.

Her work continues to be the subject of significant archival research and institutional study, including recent digital initiatives by the Getty Research Institute that document the legacy of neo-avant-garde and Fluxus scores. Her contributions remain foundational to the history of conceptual art and experimental music.