Stewart was admitted to the New York State Bar on January 31, 1977. For much of her career as a lawyer, she represented a number of economically disadvantaged clients as well as more high-profile cases. Stewart was a self-described "movement lawyer" who took a wider interest in promoting the general political interests of those she represented, rather than only dealing with the specific charges against them. Stewart defended Weather Underground member David Gilbert, who was found guilty for his role in the 1981 Brinks armored car robbery in which two police officers and a security guard were murdered.