Toussaint was born in Trinidad and Tobago and brought to live in Brooklyn in the late 1960s by her mother who was a teacher. She began her career in 1989 as a supporting performer in theatres. She gained prominence in 1991 when she was the lead actress in the critically acclaimed Lifetime television series, Any Day Now, from 1998 to 2002.
Her reputation grew as she became a regular cast in movies, including Law & Order, Crossing Jordan, Saving Grace, and Ugly Betty. Others were Friday Night, Lights, Body of Proof and The Fosters.