Born in Wakayama Prefecture, Seisho Hamachi moved to the West Coast of the U.S. in 1901, following his older brother. He attended San Jose High School in San Francisco while also working. After a teacher recognized his painting, he studied at an art school affiliated with the Boston School of Fine Arts. After graduating from the Boston School of Fine Arts, he lived and worked in New York, where he exhibited at the Society of Independent Artists in 1917, the exhibition of New York Japanese Art Association in1917and 1918, and the exhibition of Japanese Art, sponsored by New York Shimpo in 1927. He died in 1947 in Koza, Wakayama.

Reference: Tokyo Teien Art Museum, Postwar 50th Anniversary Project: Japanese American Painters: A Half Century of Hope and Suffering, 1896-1945, (exhibition catalog),Nippon Television Network Corporation (1995); Ichiro Okumura, “Seisho Hamachi: New York, Paris, Tokyo, Wakayama,” The Museum of Modern Art, Wakayama News, No.107 (2021).