Mark Verheiden was a producer and writer for Smallville. Some episodes he has written are:
- X-Ray, (directed by James Frawley) - Tina Greer's skeleton is laced with kryptonite. She is able to assume any form. She assumes the form of Lex Luthor to rob a bank. Clark Kent discovers he has x-ray vision. Lana Lang discovers her mother was much more interesting than her aunt ever told her before. And Lex Luthor turns the tables on Roger Nixon gaining himself an unwilling ally at the Metropolis Inquisitor.
- Rogue, (directed by David Carson) - Sam Phelan is a rogue cop who learns Clark's secret, but his attempts to blackmail Clark backfire when he is killed in a shootout during a museum heist. Meanwhile, Chloe Sullivan is fired as editor of the Smallville Torch, and Lex Luthor has an old girlfriend reenter his life with a plan to destroy his father.
- Shimmer, (co-written with Michael Green and directed by D.J. Caruso) - Jeff Palmer discovers a strange green rose and extracts its oils to create a cream which renders him invisible. His sister Amy Palmer is obsessed with Lex and jealous of Victoria. Jeff uses his power of invisibility to attack Victoria, but he is thwarted by Clark. Meanwhile, Clark considers making a move on Lana, as she and Whitney are having trouble.
- Zero, (directed by Michael Katleman) - Roy Rothman has come to Smallville to terrorize Lex Luthor and get vengeance for his sister, whose fiancé died at Club Zero three years ago. Meanwhile, Chloe Sullivan researches Clark's adoption and Lana Lang prepares for the opening of the Talon.
- Obscura, (co-written with Michael Green and Greg Walker, and directed by Terrence O'Hara) - Chloe is kidnapped and Lana is having visions of her attacker. Meanwhile, Lex finds a piece of the ship in Miller's Field and Clark asks Chloe to the spring formal.
- Heat, (directed by James Marshall) - Desirée Atkins uses meteor rock-enhanced pheromones to seduce Lex into marrying her and Jonathan into killing him. Clark develops a new ability: heat vision, and Lana and Chloe decide to be friends in spite of their mutual affection for Clark.
- Dichotic, (directed by Craig Zisk) - Ian Randall dates Lana and Chloe at the same time. Meanwhile, Lex meets Helen Bryce in an anger management class, and Jonathan Kent breaks his leg and argues with Martha about her job.
- Suspect , (co-written with Philip Levens and directed by Kenneth Biller) - Lionel is mysteriously shot at the Luthor Mansion, leaving behind four suspects with various motives to kill him: Jonathan Kent, Lex Luthor, Dominic Sanatori, and Ethan Miller. Lana convinces Henry Small to defend Jonathan. Clark is able to prove that Jonathan was framed.
- Witness, (directed by Rick Wallace) - Clark witnesses a robbery, but he can't stop the perpetrators. Lana finds out that Jennifer Small is seeking a divorce from Henry Small; and, Lionel offers to fund the Torch and a column at the Daily Planet.
- Perry, (directed by Jeannot Szwarc) - Perry White, a once promising journalist whose career was destroyed by Lionel Luthor, arrives in Smallville in search of alien stories for a tabloid news show. In spite of being constantly inebriated, Perry believes he has witnessed Clark using his extraordinary speed, so he devises a dangerous scheme to expose Clark's superpowers. Meanwhile, Lex learns that Perry has powerful incriminating evidence of Lionel's shady past.
- Hereafter, (directed by Greg Beeman and James Marshall) - Coach Altman is so distraught over his daughter's death that he tries to kill Lana, himself, and Megan Calder. Jordan Cross foresees their deaths and enlists the aide of Clark to thwart the plan. Meanwhile, Chloe and Lex investigate Adam Knight's mysterious background.
- Smallville: The Comic: Raptor, Chloe has been going over some of the odd events occurring in Smallville. Meanwhile, a boy named Greg Fox sets an explosive to Lex's digging site only to be caught in the blast. Due to a piece of Kryptonite present at the site, he starts to mutate into a raptor.
- Smallville #1: Paterfamilias (co-written by Clint Carpenter) - In 1989, a boy name Kenny Cavanaugh loses his father, Frank to a meteor shower. At the present time, Clark and Pete are driven to a stream by Jonathan for some fishing. On his way to leave, Jonathan is captured by Kenny (who due to the Kryptonite is able to turn invisible through means of camouflage and stealth).
- Smallville #2: Beauty (co-written by Clint Carpenter) - The Mrs. Smallville Beauty Pageant is being held, with contestant Holly Gehrig be threatened into quiting. Two suspects are mother and daughter, Brenda and Rachel. Shortly after Pete goes missing.
- Smallville #3: Chimera, Part 1 - After the recent shooting of Lionel, Lex heads to Metropolis to visit with his prep school friend, Malcolm Barnes. To his shock, he arrives to find Malcolm has been murdered and that some letters were planted to frame him for the murder. When he's held for question by the FBI, Lex discovers that his Swiss bank account is empty. He figures that his father is the only one who could have done it, and visits with him (with the intent to shoot him).
- Smallville #4: Chimera, Part 2 (co-written by Clint Carpenter) - Lex is holding up a gun to Lionel, believing that he emptied his Swiss bank account. He is shortly escorted out after discovering that his account is only now being emptied. After escaping from from the FBI (who posed as Lionel's security), Lex discovers who is behind the murder of Malcolm. He also discovers who set up the entire plan.
- Smallville #4: Phelan - Lex is given a deposition as he is need to provide info on Sam Phelan. Clark meanwhile recalls his experience with Phelan, including a moment where he committed a selfless deed.
- Smallville #5: Sojourn (co-written by Clint Carpenter) - After donning the red kryptonite ring and leaving Smallville, Clark goes to a bar in Metropolis where he fights with the patrons, and meets a girl named Chastity. After rejecting her, Clark tries to join Intergang only to be turned down. At the farm, Jonathan and Martha have to cope with Clark's absence and the damages to the farm.
- Mark wrote 11 episodes overall: 5 in Season One, 4 in Season Two, and 2 in Season Three.
- Mark wrote 7 comics, one third of the total 21 comic stories written for the Smallville comic series.
- Mark has co-written 3 episodes: one with Michael Green and Greg Walker, another with just Michael Green, and one with Philip Levens.
- Mark wrote "Rogue", the first episode of the show without a meteor freak villain (it was the ninth episode of Season One).
- Only six Season One episodes overall were not freak of the week episodes: "Rogue", "Zero", "Stray", "Nicodemus", "Obscura" and "Tempest". Of those, Mark wrote half of them ("Rogue", "Zero", "Obscura").
- Mark has written two out of the four episodes that show Clark learning new superpowers: Season One's "X-Ray", and Season Two's "Heat". The other two episodes are "Whisper" (super hearing) and "Sneeze" (super breath).
- Mark has written all of the stories that feature Sam Phelan, counting the episodes "Rogue", "Zero" and the comic story "Phelan".