.. is a genius psychologist with an expertise in body language and predominantly microexpressions and founder of The Lightman Group, a private company that operates as an independent contractor to assist investigations of local and federal law enforcement through applied psychology. Though often confronted by people's skepticism, Lightman uses any psychological technique he deems necessary to reach the truth, however elaborate or confronting. He is divorced, and has shared custody of his teenage daughter. He cares deeply about Gillian Foster, and there is a chemistry between them that has yet to develop into anything more. His mother committed suicide while he was still young, an event that led him to discovering and researching microexpressions. There is evidence he was involved with British Intelligence, due to the fact that Reynolds has said "Yeah, I read your file too. Northern Ireland? Let's talk about that...some of the crap you were involved in." He has also admitted to being an MI6 intelligence agent during the Yugoslavia Wars in 1994 in an attempt to gain the trust of an intelligence agent that he was interrogating. The character is based on Dr. Paul Ekman, a notable psychologist and expert on body language and facial expressions at University of California, San Francisco.

Dr. Lightman's colleague and co-worker in The Lightman Group. Her husband's lack of candor often challenges her open pact with Lightman: not to let their professional skill interfere with coworker's personal lives. So, when Cal believes her husband Alec is cheating on her, he simply ignores what he is seeing, much to Torres's dismay. Gillian had adopted a baby (Sophie) who was eventually returned to the birth mother. This character is based on Prof Maureen O’Sullivan, a notable psychology professor at the University of San Francisco.

initially an employee of The Lightman Group. Loker is academically educated and acquired his skills in "reading" people through practice. He also adheres to radical honesty, and thus rarely lies, even if that makes him appear rude or undiplomatic. For example, when he first meets Torres he bluntly tells her that he wants to have sex with her. Lightman demoted him to an unpaid intern after, despite Foster's warnings, he divulged sensitive information to the SEC while working on a case, calling his actions, which includes the fact that Loker made Torres lie about knowing it, "disrespectful, selfish, and just plain stupid." The first time in show he lied was the season one episode "Do No Harm," when he told Torres he "doesn't care" why a peace activist he was attracted to made up a story; Torres catches his lie and Loker acknowledges this.

an employee of The Lightman Group, and a protegee of Dr. Lightman's, who was recognized as a "natural" while she was still working as a TSA agent. Torres was abused as a child, a common pattern among naturals, by her father. Though talented and loyal, she lacks academic training and sometimes lets her emotions cloud her judgment. This was evidenced in an episode in which Cal used her emotions to cause her to disobey him, also similarly manipulating other characters, in order to solve a case.

Cal Lightman's teenage daughter. She is under shared custody between her parents, and though she does not appreciate her father's ability to "read" her, she does not deny its merit for social screening. She sometimes shows a talent for "reading" people, even her father. She has had a few boyfriends over the series that her father frequently scrutinizes. It appeared that there was chemistry between her and the character Max in "Black Friday," but in the following episode she had a new boyfriend.

an FBI agent who is assigned to and assists the Lightman Group in their investigations, offering armed assistance and practical insights.

Cal Lightman's ex-wife. She is an Assistant Attorney General and though currently engaged to another man, she also engaged in a tryst with Lightman, after he helped her in a case. It was revealed in "Truth or Consequences" that she is bi-racial, having a white mother and African-American father (the same as Beals in real life).

a Secret Service agent who becomes romantically involved with Torres. He was seriously injured during a terrorist attack. As of Season 2, no mention has been made of his whereabouts, or if he even survived.

Gillian Foster's ex-husband. He works at the United States Department of State and is a recovering cocaine addict where throughout the series it was heavily hinted that he was having an extramarital affair until it revealed the woman was his drug sponsor. He and Gillian have decided to divorce.