Ensign Murphy was a Starfleet security officer serving aboard the USS Voyager under Captain Kathryn Janeway. Murphy was stranded in the Delta Quadrant when the Voyager was forcibly brought there by the Caretaker in 2371.
In 2373, Murphy was ordered by Chakotay, to escort the Ferengi Arridor and Kol to secured quarters. The Ferengi, however, were able to knock Murphy unconscious and were able to escape, leaving Murphy with a concussion. (VOY: "False Profits")
Murphy was on duty on the bridge, working on an aft station, when the Voyager decrypted a message from Starfleet Command sent through the Hirogen communications network and when Neelix delievered the first letter from the Alpha Quadrant to Commander Chakotay. He was also present in the mess hall when Neelix delievered several more letters but received none. (VOY: "Hunters")
He accompanied Captain Janeway and another security officer into engineering where a member of Species 8472 attacked the engineering crew. He then escorted the wounded officers to sickbay. (VOY: "Prey")
He assisted too as a security guard together with Lieutenant Commander Tuvok and Damaris Cordelia to subdue a group of three Kyrians that were in engineering (holographic recreation). (VOY: "Living Witness")