Benjamin grew up in Long Island, New York, a self-described "nice Jewish girl." During her freshman year at Tufts University, she renamed herself after the Greek mythological character Medea. She received master's degrees in public health from Columbia University and in economics from The New School.Benjamin worked for 10 years as an economist and nutritionist in Latin America and Africa for the United Nations Food and Agriculture Organization, the World Health Organization, the Swedish International Development Agency, and the Institute for Food and Development Policy. She spent four years in Cuba, and has authored three books on the country.In 1988 with Kevin Danaher, her husband, and Kirsten Moller, Benjamin co-founded the San Francisco-based Global Exchange, which advocates fair trade alternatives to what she describes as corporate globalization. She is a co-founder of the left-wing feminist anti-war group Code Pink: Women for Peace, which advocated an end to the Iraq War, the prevention of future wars, and social justice. Benjamin has also been involved with the left-wing anti-war organization United for Peace and Justice.