With the impact of his dark childhood and onset of the Great Depression, Martin's early journalism career focused on deep concern for the underprivileged and forgotten, such as criminals, the impoverished, the working class, and the mentally ill. His work appeared in such publications as Saturday Evening Post, LIFE, Colliers, Atlantic Monthly, and Harper's.
Martin was hired in 1952 as a speechwriter by Illinois Governor Adlai Stevenson, and later worked on the Kennedy presidential campaign.
Martin was sent by Kennedy on a fact-finding mission to the Dominican Republic after the assassination of the dictator Rafael Trujillo in May 1961, and delivered his report in September.
"[4] Martin resigned shortly after the Kennedy assassination, on the day in which Bosch was toppled in a coup d'etat, but returned to the Dominican Republic as a special envoy in 1965 during the invasion dispatched by Johnson.
In 2008, The Library of America selected his story "Butcher's Dozen" for inclusion in its two-century retrospective of American True Crime.