Murphy was educated at the University of Wisconsin–Madison, where he studied stage, film, and television directing and earned a Master of Arts degree. After graduation he worked on the staff of Madison PBS affiliate WHA-TV. Murphy's production work on Jim Mallon's 1987 horror film, Blood Hook, led to Murphy following Mallon to Minneapolis television station KTMA, where Mystery Science Theater 3000 began airing the following year.For eleven years Murphy was a writer for MST3K; for nine of those years, he also voiced and operated the robot Tom Servo, replacing original cast member Josh Weinstein. After taking over the role of Servo, an anonymous person sent him a 6-foot-long (1.8 m) banner that read "I HATE TOM SERVO'S NEW VOICE." Flattered by the enormous amount of effort taken to heckle him, Murphy hung the banner in his office for over a year. During the final three years of the series he additionally portrayed Professor Bobo, an English-speaking mountain gorilla in the style of Planet of the Apes.
After the end of MST3K, Murphy spent the year 2001 going to a different movie every day and wrote a book about this experience, entitled A Year at the Movies: One Man's Filmgoing Odyssey. During his year at the movies, Murphy samples theatres from small-town boxes to urban megaplexes, attempts (and rejects) a theatre-food diet, suffers a kidney stone, visits both the Sundance and Cannes film festivals, sneaks Thanksgiving dinner into a showing of Monsters, Inc., and records all of these experiences, both good and bad. His feat – viewing over four hundred films on four continents – was mentioned in Ripley's Believe It or Not. Murphy holds a BA in journalism from the University of Utah and an MA in directing for the stage and screen, from the University of Wisconsin–Madison.
In 2014, RiffTrax published Kevin Murphy's list of favorite riffs. They included: