Adam Jensen – The player's character, voiced by Elias Toufexis. Adam was a SWAT commander in the Detroit Police, but his career came to an end when he refused to follow a questionable order. Subsequently, Adam became a private security specialist for Sarif Industries, assigned to protect scientists on the verge of cutting edge breakthroughs. During what should have been a routine security detail, an ambush by a rogue black ops team, the Tyrants, leaves Adam critically injured and his charges dead. Adam awakens with cybernetic augmentations, and begins a relentless search for the truth behind the attack.
David Sarif – The founder and CEO of Sarif Industries, David is a futurist who developed an interest in machines at an early age. He is known for his forward, honest demeanour, though he has no aversion to keeping secrets when appropriate.
Bill Taggart - A psychologist, Bill is the founder of the Humanity Front and becomes a leading opposition to human augmentation, a cause he took up after his wife's murder by an augmented addict.
Hugh Darrow - The godfather of Augmentation, after having retired, builds Panchaea to help control global warming. Seen as a hero for David and Megan, however, it is revealed that he regrets creating augmentation and plans to end bio-modification in a rather sinister way.
Zhao Yun Ru - One of the primary antagonists, she is the president of Tai Yong Medical, a rival company against Sarif Industries whose company is attempting to take control of the bio-modification market.
Dr. Megan Reed - One of the lead researchers at Sarif Industries and Adam's ex-girlfriend. Dr. Reed is considered a pioneer in the field of human enhancement technologies. However, dedication to her research and an aloof demeanour has made it difficult for her to cultivate lasting interpersonal relationships.
Faridah Malik - A helicopter pilot for Sarif Industries, she transports Jensen into various missions and locations. In one of the side missions, Malik asks Jensen to help her find the murderer of her best friend in Hengsha and bring him to justice.
Frank Pritchard - The head of Sarif's cyber-security team, Frank has a sour relationship with Jensen, however, he is Jensen's main logistical support during his missions.
Eliza Cassan - A reporter for the international news network, Picus TV. She shows interest in Jensen and his activities and supports him in uncovering the conspiracy.
Isaias Sandoval - Taggart's chief aide, who joins the Humanity Front after his augmented brother goes on a rampage and is talked down by Taggart.
Lawrence Barrett - A former marine turned mercenary, Barrett is a member of the Tyrants. Like Namir, he has augmented his already impressive physique with numerous cybernetic upgrades. He lives for the moment when he's beaten his enemy into submission, and Adam Jensen is his next target.
Vasili Sevchenko - Ukrainian scientist at the Sarif Industries' labs.
Yelena Fedorova - A statuesque, athletic woman of Afro-Russian descent, Yelena is one of Belltower's most elite assassins. Unlike Barrett, she favours stealth over brute force. Being one of few women in a male-dominated profession has strongly influenced her world view, making her cautious of everything around her.
Jaron Namir – An Israeli-born mercenary, Namir is the field commander for the Tyrants. Officially a senior member of the PMC Belltower Associates, he actually takes his orders from the Illuminati. A merciless combatant, yet also a devoted family man, he has had numerous cybernetic enhancements to compensate for the decline associated with advanced age.
Tong Si Hung - The biggest crime boss in Hengsha, Tong owns a nightclub called The Hive. Later he is revealed to be the leader of the Harvesters, a gang who deals in black market human enhancement augmentations as well as being the father of Tracer Tong, a character in the original Deus Ex.
Zeke Sanders - A former augmented soldier, Zeke is the leader of the anti-augmentation extremist group, Purity First, who leads an attack on a Sarif manufacturing plant.