As a young man, in 1964 and early 1965, Ewen was a field secretary for the civil rights organization the Student Nonviolent Coordinating Committee (SNCC). After working as a volunteer in the Freedom House in Columbus, Mississippi, he became part of the SNCC staff, earning the standard pay of $9.66 per week. After working in Columbus, he and Isaac Coleman, who was the project director, opened up a new field office in Tupelo, Mississippi. In 1966, Ewen was one of the founding editors of an early underground newspaper, ''Connections'', in Madison, Wisconsin, where he was a student.
In 1989, his book ''All Consuming Images'' provided the basis for Bill Moyers' four-part award-winning series, "The Public Mind." In 2004, another of his books, ''PR! A Social History of Spin'', was the foundation of a four-part BBC series, "The Century of the Self," produced by Adam Curtis. "PR!" also provided the foundation for the 2018 French documentary, "Propaganda: La fabrique du consentement," directed by Jimmy Leipold and produced by Arte Television and INAfr. It was also the foundation of a 2020 Russian television documentary, "Стюарт Юэн. PR: как создается правда?"
Ewen has become a spokesman against violations of academic freedom in the period since 9/11, and is the Chairman of the Board of Directors of the Frederic Ewen Academic Freedom Center at NYU, which is named after his great uncle, a professor at Brooklyn College who was forced to resign after refusing to testify before HUAC.