Paskey credits the longevity of his character to his sense of caution. Since he was on the set most of the time and knew the script well, he made sure that he was always elsewhere when an episode called for someone to die. When his character does die in the episode "Obsession," Paskey explains his mysterious return in the next episode by describing a lost scene, where Dr. McCoy administered a miracle potion that saves Leslie's life, that ended up on the cutting room floor.
In "This Side of Paradise" his is the only character to mutiny openly against his superior, Captain Kirk, and even disobeys orders again in "And the Children Shall Lead," although under an alien influence. In "The City on the Edge of Forever," Paskey was the driver of the truck in the scene where character Edith Keeler (Joan Collins) is struck down and killed.
Paskey also appeared occasionally as a stand-in for Shatner in certain long scenes. He was the hand-double for James Doohan, who was missing a finger, in "Wolf in the Fold" and "That Which Survives." He appeared in most of the episodes from the first two seasons of the original series. A bad back and cluster headaches from an old injury, which worsened from the set lighting, led to his leaving the show in the third season. Paskey admitted in a July 1988 Starlog Magazine interview that once the pain had gone, he tried to return to acting but had lost many of his Hollywood contacts while working on Star Trek, and eventually retired from the profession.
| No. | Episode name | Role | Talks | Credit | Remarks |
|---|---|---|---|---|---|
| 00 | Where No Man Has Gone Before | crewman | no | no | seen behind Kirk and Spock while they engage in Tri-D Chess |
| 1 | The Man Trap | Lt. Ryan | no | no | as helmsman and medical assistant |
| 2 | Charlie X | crewman | no | no | |
| 4 | The Naked Time | Lt. Ryan | yes | no | escorted, for being drunk, away from bridge station |
| 5 | The Enemy Within | crewman | no | no | freezing with Sulu and landing party |
| 6 | Mudd's Women | Conners | no | no | caught, and reproached by Dr. McCoy, for ogling Ruth Bonaventure |
| 7 | What Are Little Girls Made Of? | crewman | no | no | as bridge engineer |
| 9 | Dagger of the Mind | crewman | no | no | as bridge engineer & wayward eaves dropper |
| 10 | The Corbomite Maneuver | crewman | no | no | as bridge engineer, also seen on lower decks |
| 11 | The Menagerie, part 1 | crewman | no | no | as bridge engineer, witnesses Spock's arrest |
| 13 | The Conscience of the King | crewman | yes | no | as helmsman, with no rank insignia |
| 14 | Balance of Terror | Mr. Leslie | no | no | as bridge engineer |
| 15 | Shore Leave | Mr. Leslie | no | no | as helmsman in opening prologue only |
| 16 | The Galileo Seven | crewman | no | no | on bridge and in transporter room, always faceless |
| 17 | The Squire of Gothos | Lt. Leslie | no | no | in captain's seat, now with Lt's. insignia |
| 18 | Arena | Lt. Leslie | no | no | as bridge engineer |
| 19 | Tomorrow is Yesterday | Lt. Leslie | no | no | as bridge engineer |
| 21 | The Return of the Archons | Lt. Leslie | no | no | joins landing party, seen being awakened by Kirk |
| 22 | Space Seed | Lt. Leslie | no | no | dines at "Welcome to the 23rd Century" dinner for Khan |
| 24 | This Side of Paradise | Lt. Leslie | yes | yes | as "crewman", first time Leslie disobeys Kirk's orders, by mutinying |
| 25 | The Devil in the Dark | Lt. Leslie | no | no | as security and possible horta target |
| 27 | The Alternative Factor | Lt. Leslie | yes | yes | as "Lesley", sits in the command seat at beginning of last scene |
| 28 | The City on the Edge of Forever | Lt. Leslie | no | no | as science officer |
| 29 | Operation: Annihilate! | Lt. Leslie | no | no | as transporter chief, gets Vulcan nerve pinch |
| 30 | Amok Time | Lt. Leslie | no | no | as bridge engineer and medical assistant |
| 31 | Who Mourns for Adonais? | Lt. Leslie | no | no | Sulu and Leslie scan for Apollo's power source |
| 32 | The Changeling | Lt. Leslie | no | no | as navigator in braided yellow command shirt |
| 33 | Mirror, Mirror | Lt. Leslie | no | no | briefly in prologue and epilogue |
| 34 | The Apple | Lt. Leslie | no | no | as bridge engineer |
| 35 | The Doomsday Machine | Lt. Leslie | no | no | as bridge engineer |
| 36 | Catspaw | Lt. Leslie | no | no | as bridge engineer and helmsman |
| 38 | Metamorphosis | Lt. Leslie | no | no | with Scotty when Kirk checks in |
| 39 | Journey to Babel | Lt. Leslie | no | no | as bridge engineer |
| 40 | Friday's Child | Lt. Leslie | no | no | as bridge engineer |
| 41 | The Deadly Years | Lt. Leslie | no | no | as bridge engineer |
| 42 | Obsession | Lt. Leslie | no | no | dies of asphixiation |
| 43 | Wolf in the Fold | Lt. Leslie | no | no | on bridge, gets tranquilized with crew |
| 44 | The Trouble With Tribbles | Lt. Leslie | no | no | bridge, security, adopts a tribble from Uhura |
| 45 | The Gamesters of Triskelion | Lt. Leslie | no | no | as bridge engineer and science officer |
| 46 | A Piece of the Action | Lt. Leslie | no | no | as bridge engineer |
| 47 | The Immunity Syndrome | Lt. Leslie | no | no | also security in transporter room, "yellowshirt" on lower decks |
| 48 | A Private Little War | Lt. Leslie | no | no | as bridge engineer |
| 49 | Return to Tomorrow | Lt. Leslie | no | no | also as security officer on transporter |
| 50 | Patterns of Force | Ekosian | no | no | as Nazi officer; also a second character with mustache |
| 51 | By Any Other Name | Lt. Leslie | no | no | dehydrated into a polyhedron |
| 52 | The Omega Glory | Lt. Leslie | no | no | on Bridge; and guard, arresting Tracy |
| 53 | The Ultimate Computer | Lt. Leslie | no | no | escorts a stunned Dr. Daystrom to sickbay with another security officer |
| 54 | Bread and Circuses | Lt. Leslie | no | no | |
| 55 | Assignment: Earth | Lt. Leslie | no | no | stunned by Gary Seven |
| 57 | The Enterprise Incident | Lt. Leslie | no | no | a most happy Leslie, seeing that Kirk is alive |
| 59 | And the Children Shall Lead | Lt. Leslie | no | no | second time Leslie disobeys Kirk's orders |
| 60 | Is There in Truth No Beauty? | Lt. Leslie | no | no | as security |
| 61 | Spectre of the Gun | Lt. Leslie | no | no | as bridge engineer, prologue only |
| 68 | Elaan of Troyius | Lt. Leslie | no | no | kindly offered his seat to the Dohlman, even though he needed it to work |
| 503 | Trials and Tribble-ations | Lt. Leslie | no | no | on Deep Space Nine, as security |
Paskey admitted that he considered auditioning for 1979's Star Trek: The Motion Picture but later reconsidered. He remained a fan of the film series but not the television follow-up Star Trek: The Next Generation, as he explained that "he went to sleep on it." In 2004, he did appear in the Star Trek: New Voyages episode "Come What May" as Admiral Leslie, a character established as Lieutenant Leslie's father.