He is best known for his work on the history of American individualist anarchism, Men Against the State, first published in 1953. His 1964 book American Liberalism and World Politics, 1931-1941 is also well known.
He was a close associate of historian Harry Elmer Barnes. Martin's own views were libertarian and individualist anarchist. He was also an egoist influenced by Max Stirner, and rejected the natural rights views held by some other libertarians. His work was praised by liberal historian William Appleman Williams, libertarian theorist Murray Rothbard, and others. After a teaching career at several universities, he took a job teaching at Robert LeFevre's Rampart College, assuming it would be a full-time job. This was not the case as Rampart College was not yet really a college but only a series of workshop/lectures on libertarian political economy. This led to an eventual falling out between Martin and LeFevre when Rampart College went out of business three years after Martin was hired, with Martin charging LeFevre with a breach of his five year contract.
In 1968 after Rampart College folded, Martin founded the small Ralph Myles Publishing, which reprinted Men Against the State and brought a series of classic anarchist writings back into print, most notably No Treason: The Constitution of No Authority by Lysander Spooner. Martin also was the author of books on anti-war subjects including Revisionist Viewpoints, a collection of anti-World War II essays, and An American Adventure in Bookburning, a history of censorship in the United States during World War I.
Starting in 1979 Martin began to associate with the Institute for Historical Review, a Holocaust denial group, severely undercutting, in the minds of some, his previous credibility as a historian. One of his last books was The Man Who Invented Genocide: The Public Career and Consequences of Raphael Lemkin published in 1984.