Marshall was born Everett E. Grunz in Owatonna, Minnesota.

From 1974 to 1981, E.G. Marshall hosted the nightly radio drama The CBS Radio Mystery Theater (or ), which ran on CBS radio affiliate stations across the United States. CBSRMT was an ambitious and sustained attempt to revive the great drama of old-time radio.

Each episode began with the ominous sound of a creaking door, slowly opening to invite listeners in for the evening's adventure. At the end of each show, the door would swing shut, with Marshall signing off, "Until next time, pleasant...dreams?"

E.G. Marshall hosted the program every year but the final one, when actress Tammy Grimes took over.

He died of lung cancer in Bedford, New York.