Foscarinis grew up in a middle-class, Greek immigrant family in Manhattan, New York.
Foscarinis graduated from the New Lincoln School, received a B.A., magna cum laude, from Barnard College of Columbia University, where she was elected to Phi Beta Kappa; a Master of Arts (in Philopsophy) from the Graduate School of Arts and Sciences at Columbia University, where she was a John Dewy Fellow; and a J.D.
Before entering the advocacy field, Foscarinis was a law clerk at the U.S. Court of Appeals for the Second Circuit from 1981 to 1982.
[1] In 1985, Foscarinis left her job at the law firm and established and directed the Washington, D.C., office of the National Coalition for the Homeless.
She has campaigned for recognition of the human right to housing in the United States; she has written[4][5][6][7] extensively on homelessness and on legal rights of homeless people, for both general and legal audiences in U.S. and international publications.