Miles is introduced early in the fourth season as a hotheaded and sarcastic medium as a crew member aboard the freighter called the Kahana that is offshore the island where most of Lost takes place.

In early December 2004, when he is twenty-seven years old, Miles is hired for $1.6 million by Charles Widmore to go on a freighter called the Kahana to an uncharted island to retrieve a mass murderer named Ben Linus, as Widmore believes that Miles will be able to communicate with those whom he had killed and gain information regarding his location.

The next day on the island, Miles encounters the survivors of the September 22 Oceanic Airlines Flight 815, who are believed to be dead by the world at large.

The survivors settle in 1974, by which point only Miles, Faraday, former Other Juliet Burke (Elizabeth Mitchell) and 815 passengers James "Sawyer" Ford (Josh Holloway) and Jin Kwon (Daniel Dae Kim) remain; Rose Henderson (L. Scott Caldwell), Bernard Nadler (Sam Anderson) and Vincent the dog (Pono) also survive, but they are physically separated and do not meet any of them again for three years until July 1977.

Miles and his group move into the Barracks and pseudonymously join the DHARMA Initiative, an organization conducting scientific research while living there that would eventually be purged in 1992 by Ben and the Others.

Despite the option to board the DHARMA submarine and "go back to the real world", the survivors from 2004 stay on the island together in the hope that they can somehow return to the time that they knew.

The next morning, Faraday comes clean to Chang that they are from the future and warns of a catastrophic "incident" that is due to occur at the building site for the Swan, DHARMA's planned island station dedicated to electromagnetism.

The antagonistic DHARMA members engage in a gunfight with Jack, believing him to be an Other, and Miles, Sawyer, Juliet, and Kate come to his aid.

When the Swan site goes haywire, Chang's arm is caught in the debris and Miles rushes to his side, saving him and calling him "Dad".

After he tells his father to run as far as possible from the site, the bomb is detonated and everything goes to white, leaving Miles's status uncertain.

When Kate, Jack, Hurley and Jin go to the temple to save Sayid, Sawyer asks Miles to remain behind to help bury the now-deceased Juliet and to use his power to find out what she was trying to tell him before she died.

Ben is spared, however, and Miles then digs up Nikki and Paulo's diamonds where they had been buried with them to compensate for his lack of money on the Island.

Miles decides to follow Richard and Ben, telling Hurley that he has seen "that thing in action," and that it doesn't want to talk.

He later gains access to James' credit card account and learns his partner did not go to Palm Springs like he said, instead going to Australia.

Miles is hotheaded and initially hostile toward the survivors,[1] after one of them kills his colleague Naomi Dorrit (Marsha Thomason).

[4] Ken Leung claims that he is often approached by people who like the character and he assumes that it is because of Miles's "sardonic wit" and "devil-may-care sort of attitude.

[7] Leung stated that "He seems haunted by something, that—that's for sure … one of the first thoughts I had [was that his] communication with the dead … can't be a great thing … it's not a happy skill to have."

"[8] The day after the April 22, 2007 episode of The Sopranos titled "Remember When" aired, Lost's co-creator Damon Lindelof met with fellow executive producer/writer/show runner Carlton Cuse and said that "there's an actor on th[e] show [last night]—I'm not going to tell you who he is—and I wonder if he has the same impression on you that he had on me".

[9] Cuse correctly guessed Ken Leung,[10] who had guest starred as one-time character Carter Chong, a young and angry mental patient.

"[12] Leung believed that he was auditioning for the role of Russell, a "brilliant mathematician" in his late thirties with immense knowledge across various scientific fields, limited social skills and broken personal relationships.

[13] Leung was the only actor who tried out for this part, as writers had written the role of Miles for him; had he not accepted the job, the character would have been completely rewritten.

Costume designer Roland Sanchez based Miles's wardrobe choice after that of The Rolling Stones member Keith Richards; specifically a picture in which he wore a sleeveless vest.

Sanchez believed that Miles fit the haggard look and bought an Armani Exchange jacket, cropped the sleeves and added a hood.

This influenced the way that it was revealed in the show, as the writers looked for a way to present the information in a way that would both be interesting to those who had not guessed it and not insulting to viewers who had been predicting it.

After four appearances, Leung was nominated for the J. C. Penney Asian Excellence Award in the Supporting Television Actor category,[20] but he lost to Rex Lee, who plays Lloyd on HBO's Entourage.

[24] Diane Werts of Newsday thought that "Ken Leung and Michael Emerson may be the two current most interesting actors in this mix".

[25] Alan Sepinwall of The Star-Ledger commented that "Miles the dustbusting ghostbuster is easily my favorite [of the characters introduced in 'Confirmed Dead'] … why not throw in a medium [among the show's science fiction phemonena] … I love the sarcastic energy he brings.

[26] After Miles' introduction in the second episode of the fourth season, Jeff Jensen of Entertainment Weekly wrote that Leung made "a strong impression" and was well cast.

[27] Chris Carabott of IGN stated that "Leung does an adequate job of getting Miles' arrogant brand of confidence across.