Marrs was a important figure in the JFK conspiracy press and his book "Crossfire" was a source for Oliver Stone's movie "JFK". He wrote books asserting the existence of government conspiracies regarding aliens, 9/11, telepathy, and secret societies. He was once a news reporter in the Dallas–Fort Worth Metroplex and taught a class on the assassination of John F. Kennedy at University of Texas at Arlington for 30 years. Marrs was a member of the Scholars for 9/11 Truth.