By then he had already taken part in anti-war protests and had become a founder and editor of the Washington Free Press, an alternative bi-weekly newspaper which did not last long. In 1969, he wrote and published an exposé of the CIA in which were revealed the names and addresses of more than 200 CIA employees. He worked as freelance journalist in the United States, Europe and South America. In 1972–1973, Blum worked as a journalist in Chile where he reported on the Allende government's "socialist experiment". In the mid-1970s, he worked in London with ex-CIA officer Philip Agee and his associates "on their project of exposing CIA personnel and their misdeeds". He supported himself with his writing and speaking engagements on college campuses. One of Blum's stories on Iraq was listed by Project Censored as one of "The Top Ten Censored Stories of 1998" In his books and online columns, Blum devoted substantial attention to CIA interventions and assassination plots. Noam Chomsky has called Blum's book Killing Hope: U.S. Military and CIA Interventions Since World War II, "far and away the best book on the topic." Blum supported Ralph Nader's presidential campaigns. He circulated a monthly newsletter by email called "The Anti-Empire Report". Blum described his life's mission as: "If not ending, at least slowing down the American Empire. At least injuring the beast. It's causing so much suffering around the world." In an interview with C-SPAN in 2006, Blum stated: "Speaking about U.S. foreign policy, which is my specialty, the authors I would most recommend would be Michael Parenti and Noam Chomsky and Edward Herman and Howard Zinn and Alexander Cockburn."
In early 2006, Blum briefly became the subject of widespread media attention when Osama bin Laden issued a public statement in which he quoted Blum and recommended that all Americans read . As a result of the mention, sales of his book greatly increased. "I was quite surprised and even shocked and amused when I found out what he'd said," Blum commented. "I was glad. I knew it would help the book's sales and I was not bothered by who it was coming from. If he shares with me a deep dislike for certain aspects of US foreign policy, then I'm not going to spurn any endorsement of the book by him. I think it's good that he shares those views and I'm not turned off by that." On the Bin Laden endorsement, Blum stated, "This is almost as good as being an Oprah book." In an interview on MSNBC Countdown, he said: "Basically it's US foreign policy which creates anti-American terrorists. It's the things we do to the world. It's not, as the White House tells us, that they hate our freedom and democracy. That's just propaganda." In a May 22, 2006 article entitled "Come Out of the White House With Your Hands Up", Blum wrote: "Since the bin Laden recommendation, January 19, I have not been offered a single speaking engagement on any campus.... This despite January–May normally being the most active period for me and other campus speakers."
