This is a list of fictional characters in the television series The 4400. The list includes the series main characters, recurring characters, minor characters, as well a list of the 4400 returnees.

Tom Baldwin, portrayed by Joel Gretsch, is the series's main protagonist. Tom was formerly at the FBI, and a longtime friend of Dennis Ryland. He joined Ryland at NTAC, but left after 5 months to investigate the circumstances surrounding his son, Kyle Baldwin, being comatose. He employed private investigators to find his missing nephew Shawn Farrell, in an attempt to discover the truth. Kyle's comatose state places great strain on Tom's marriage to Kyle's mother, Linda, and at some point before the Pilot the two have separated.

Kyle Baldwin, portrayed by Chad Faust, is Tom and Linda's son and Shawn Farrell's cousin. He is possessed by a human being from the future, who reveals he was supposed to act as a communication channel between the future and Tom, to guide him in his dealings with the returned 4400 as they attempt to avoid the catastrophe that has caused humans to largely die out. He is responsible for the murder of Jordan Collier and spends several months in prison. He takes promicin to gain healing abilities but instead developed an imaginary guide that assumed the appearance of a woman named Cassie Dunleavy. At the end of the series he convinces his father to also take a promicin shot.

Jordan Collier, portrayed by Billy Campbell, is one of the central figures of the 4400. Intelligent and persuasive, he quickly recognized the 4400 and their situation as being on a war footing with the government. Although his motives and means change during the course of the series from greed to altruism, Jordan's greatest wish appears to be that he will be remembered as a hero who changed the world, in the eye of the future. Jordan Collier's ability to neutralize promicin is discovered in "The Wrath of Graham" when he strips Graham Holt of his ability. It is theorized that this ability only works on promicin-positive non-4400s. Jordan Collier and Danny Farrell have the exact opposite ability.

Collier was initially described to Campbell as an "interesting" character rather than as a villainous role, a characterization that Campbell believes that the writers stuck with. Eric Goldman of IGN described Collier as "a fascinatingly morally ambiguous figure; one who seems like a Jesus figure one moment and nearly genocidal in another". Campbell himself has described the character as "a sociopath" and "ever manipulative".

Shawn Farrell, portrayed by Patrick Flueger, was born December 12, 1983, and disappeared April 22, 2001 from Highland Beach near Seattle, Washington, while with his cousin Kyle Baldwin. Shawn was not intended to be a 4400; as Kyle and Shawn are drinking at the beach, Shawn witnesses Kyle in the act of being abducted, and in an effort to help him, interrupts the process and is taken instead. Shawn has the ability to control the flow of life in living organisms, usually manifesting itself through healing physical damage done to the bodies of others. Limits for this power are unclear; although he is capable of basic healing, having successfully healed broken bones, severe burns and even a mortal stab through the chest, but is later able to heal people with cancer and all sorts of diseases. His ability is by close proximity - he tends to touch his targets, but can heal through clothing. When threatened he can reverse his power and drain the life-force from others, effectively killing them. He uses this latter ability to drive a possessing entity out of Kyle, and in a vision of the future he witnessed – in which, the catastrophe itself ripped the United States apart – he kills Richard Tyler, in apparent retaliation for Richard's pre-emptive strike (against whom has not yet been explicitly revealed). He is also forced to use this ability on his brother Danny as a mercy killing.

Nina Jarvis, portrayed by Samantha Ferris, became the director of NTAC in season two after succeeding Dennis Ryland; Ryland took his role back temporarily while Nina recovered from a gunshot wound. Nina returned as the director of NTAC after recovering from her injuries. Nina was later dismissed and replaced by Meghan Doyle.

Alana Mareva, portrayed by Karina Lombard, was born October 17, 1969, in Tahiti, and disappeared September 5, 2001, from Seattle, Washington. Prior to her abduction, her husband and only son Billy had been killed by a drunk driver. She was an artist who owned an art gallery and travelled the world to purchase pieces for display there. Alana can telepathically create a completely realistic subjective alternate reality that she and a person with whom she is in physical contact can perceive. The reality can incorporate ideas from Alana or from her subject and is normally indistinguishable from objective reality. A great deal of time can pass in such realities while very little objective time passes. There is evidence that subjective realities of long duration accumulate subtle errors that permit the subconscious of the subject to recognize them for what they are. Tom Baldwin eventually realized that he was in subjective reality because of such errors. Alana was at that time subjected to the effects of the promicin-inhibitor. Most 4400s developed their abilities or refined their control when no longer dosed with the inhibitor. In season three, Diana Skouris was able to remain in the alternate reality without Alana. It was revealed by that incident that a participant in the alternate reality must be consciously willing to leave it.