Vachss has worked as a federal investigator in sexually transmitted diseases, a caseworker in New York, and a professional organizer. He was the director of an urban migrants re-entry center in Chicago and another for ex-cons in Boston. After managing a maximum-security prison for violent juvenile offenders, he published his first book, a textbook, about the experience. He was also deeply involved in the relief effort in Biafra, now Nigeria.
For ten years, Vachss' law practice combined criminal defense with child protection, until, with the success of his novels, it segued exclusively into the latter, which is his passion. Vachss calls the child protective movement "a war," and considers his writing as powerful a weapon as his litigation.