Balch was born to a prominent Yankee family in Jamaica Plain, Massachusetts, a neighborhood of Boston, to Francis V. and Ellen (nėe Noyes) Balch. Her Father was a successful Lawyer and one time secretary to United States Senator Charles Sumner. She graduated from Bryn Mawr College in 1889 after reading widely in the classics and languages, and focusing on economics. She did graduate work in Paris and published her research as Public Assistance of the Poor in France (1893). She did settlement housework in Boston, but decided on an academic career.
She then studied at Harvard University, the University of Chicago, and the University of Berlin, and began teaching at Wellesley College in 1896. She focused on immigration, consumption, and the economic roles of women. She served on numerous state commissions, such as the first commission on minimum wages for women. She was a leader of the Women's Trade Union League, which supported women who belonged to labor unions. She published a major sociological study of Our Slavic Fellow Citizens in 1910.
She moved into the peace movement at the start of World War I in 1914, and began collaborating with Jane Addams of Chicago. She became a central leader of the Women's International League for Peace and Freedom (WILPF) based in Switzerland, for which she won the Nobel Peace Prize in 1946.
Her major achievements were just beginning, as she became an American leader of the international peace movement. In 1919, Balch played a central role in the International Congress of Women. It changed its name to the Women's International League for Peace and Freedom, and was based in Geneva.
Balch converted from Unitarianism and became a Quaker in 1921. She stated, "Religion seems to me one of the most interesting things in life, one of the most puzzling, richest and thrilling fields of human thought and speculation... religious experience and thought need also a light a day and sunshine and a companionable sharing with others of which it seems to me there is generally too little... The Quaker worship at its best seems to me give opportunities for this sort of sharing without profanation."
She won the Nobel Peace Prize in 1946 for her work with the Women's International League for Peace and Freedom (WILPF). Her acceptance speech highlighted the issues of nationalism and efforts for international peace. Balch never married. She died the day after her 94th birthday.