[2] She lived in Lompoc as a teenager,[3] and graduated from the University of California, Berkeley with a BA in home economics in 1938.

[4][5] In 1942, Kyogoku and her family were interned at the Topaz War Relocation Center by the U.S. government due to Executive Order 9066.

While in Philadelphia, Hasegawa began work with the Women's International League for Peace and Freedom (WILPF), a peace-seeking non-governmental organization that had vehemently opposed the internment of Japanese Americans and helped to relocate and readjust freed Japanese.

[11] She moved to South Hadley, Massachusetts in 2001, where she continued to be active in working for peace and inter-religious cooperation until her death on July 1, 2012.

In 2012, a documentary, Marii Hasegawa: Gentle Woman of a Dangerous Kind, was shown at film festivals.