Born on a farm near Sheldon, North Dakota, the grandchild of Irish Catholic homesteaders, McGrath was educated at the University of North Dakota, Louisiana State University, New College, and Oxford University, the latter as a Rhodes Scholar. He was in the U.S. Air Force in the Aleutian Islands during World War II, isolated from combat in a unit full of radicals feared by the high command. He moved to Hollywood on his return and married Alice Greenfield (McGrath), a communist organizer in Los Angeles who is the real social worker behind the heroine of Luis Valdez's play (and later film) Zoot Suit. In 1953, at the height of the long postwar inquisition that culminated in the McCarthy Era, McGrath was teaching at Los Angeles State College when he was called before the House Un-American Activities Committee. Citing his constitutional guarantees of free speech and political association—guarantees the government swept aside—McGrath refused to answer the committee's questions about his own beliefs or to betray his friends. "Poets have been notorious non-cooperators where committees of this sort are concerned," he added, "I do not wish to bring dishonor upon my tribe." McGrath was fired from his teaching job and blacklisted as a result. A lifelong socialist and prairie populist, veteran of failed farms during the Great Depression, and occasional welder and logger, McGrath then pieced together a living doing labor organizing, writing scripts for documentary films, and eventually, when the inquisition had run its course, by teaching. In 1975 he was investigated by a grand jury for possible third-degree murder in the shooting death of a Minnesota man; though the jury returned a no-charge verdict, the incident hurt him deeply. Through it all, he remained a revolutionary and an ironist, writing short poems notable not only for their rhetorical intricacy and political wit but also for their passionate commitment to justice and sanity. He would also write one of the great American book-length poem sequences, Letter to an Imaginary Friend, finally issued in its entirety posthumously in 1997.