|Born||September 17, 1918
|Died||July 1, 2012
South Hadley, Massachusetts
|Education||BA from University of California at Berkeley in 1938|
|Known for||peace activist, national president of the Women's International League for Peace and Freedom 1971 - 1975|
Marii Hasegawa (September 17, 1918 – July 1, 2012) was a peace activist, known for her fifty years of work with the Women's International League for Peace and Freedom, including serving as its president during the Vietnam War.
Hasegawa was born in Hiroshima, Japan. Her family moved to the United States in 1919, after her father, a Buddhist priest, was assigned to serve Buddhists in California. She graduated from the University of California, Berkeley with a BA in home economics in 1938.
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. She would hold varying roles within WILPF for the next fifty years, such as the chair of its Membership and Extension Committee from 1960 to 1965, its consultant to committees from 1965 to 1968, and its national president from 1971 to 1975. Her presidency of the organization was during the Vietnam War. Hasegawa organized protests against the war and led a peace delegation to North Vietnam. 
Hawegawa received the Niwano Peace Prize in 1996. 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.
- "Marii K. Hasegawa". genealogy bank. Retrieved 13 October 2013.
- Gilhool, Gillian (2004-03-22). "Generations of courage: Japan and the legacy of World War II. (Niwano Peace Foundation)". Women's International League for Peace and Freedom. Retrieved 2009-05-17.
- "Women's International League for Peace and Freedom Collect, PART III: U.S. SECTION, Series A, 4, 1960-1999 -- Part 1: Committees". Swarthmore College. Retrieved 2009-05-17.
- "Past Presidents Recommend Selling WILPF Building in Philadelphia". Women's International League for Peace and Freedom. Retrieved 2009-05-17. Check date values in:
- Brinson, Betsy. "History and Archives: The Vietnam Summer Project". Retrieved 2009-05-17.