Mary Fels was born to a German-Jewish family in Bavaria. They emigrated to the USA in 1869 and Mary grew up in Iowa, where her father made his living selling dry goods. She graduated from Keokuk High School, and then spent one year at St. Mary’s Academy in Notre Dame, Indiana. She also attended the University of Pennsylvania in Philadelphia, where she met Joseph Fels, a distant cousin. In 1881, they married and had one child. The couple had homes in both Philadelphia and in London, where Joseph Fels and his brothers operated an extremely successful soap manufacturing company. When Joseph Fels died in 1914, Mary moved to New York City and used her inheritance from her husband to become extremely active in a variety of charitable and political causes. She wrote her husband's biography, Joseph Fels: His Life Work (1916). During World War I, she served as the editor of The Public: A Journal of Democracy, and wrote a number of editorials supporting President Woodrow Wilson, encouraging labor unions, urging better treatment for African-Americans, and backing the right of women to vote. After the British Mandate was established in Palestine, she wrote about the need to establish a Jewish state and donated to many Jewish charities there. Her book Toward the Light (1929) reiterated her commitment to social justice.