As a vampire
Upon becoming a vampire, Knight gained several supernatural abilities and weaknesses, many commonly associated with vampires, and some original to the series.
As a vampire, Knight possess enhanced senses; infrared vision, enhanced hearing, superhuman strength, preternatural speed and agility, is able to regenerate critical wounds over small amounts of time, and is able to fly. His body is also very resilient to the elements, being immune to the effects of cold, poison, illnesses and diseases, and his heart beats only three times per 10 minutes. One of his most useful powers is the ability to perform hypnosis on some, but not all people (those able to resist hypnosis are known as resisters), which will help several times during his work with the Metropolitan Toronto Police. Amongst his weakness are a deadly aversion to sunlight, violent allergic reactions to foods (but not all liquids), an allergy to smelling garlic, a compulsion to look away from Holy objects and religious symbols, and coming into contact with crucifixes and holy water will cause his flesh to burn. Like others vampires in fiction, Knight is immortal, he does not physically age beyond the point of his vampire transformation nor is he vulnerable to the effects of old age or natural death, but can be killed by exposure to sunlight, having a wooden stake driven through his heart, fire, or decapitation.
Knight appears human in normal circumstances, although he rarely perspires – and when he does, he does not perspire sweat, but rather blood – and his skin is cold to the touch. Knight will reveal his vampire traits when threatened, or when becoming aggressive. This is known as vamping out by the fans of the series, but it is never referred as such during the series. When taking a vampire aspect, Knight's eyes turn yellow, and bares the stereotypical vampire fangs. Amongst the common vampire traits found in fiction, Knight does not possess the ability to shapeshift into a bat, and is not inclined to sleep in a coffin. He also does not lose any of his vampire abilities upon at dawn, although exposure to sunlight is still fatal.
In the Forever Knight universe, vampires rarely stay more than a few years in one place in order to keep their true identities concealed. He thus engages in centuries of killings and murders accompanied by Janette and LaCroix. Janette and Knight were lovers, but Janette ended it; while Knight was initially devastated, he eventually accepted her decision and remain on good terms with her. After centuries of indiscriminate killing, Knight started to feel guilt and resolves to only kill those who deserved death. He also has regrets over his choice to become a vampire, and desires to regain his mortality and humanity. Knight will spend most of the Forever Knight series trying to find a way to become human once again. This is met with amusement from other vampires, but LaCroix finds these thoughts unacceptable; this difference of opinions will be the source of great conflicts between the two over the span of the entire series.
Over the series Knight is seen with several historical figures such as Joan of Arc, Arthur Conan Doyle, Ludwig van Beethoven, Jack the Ripper, Grigori Rasputin and Adolf Hitler. LaCroix and Knight, being bonded by blood, also share a psychic bond and are able to sense each other over short distances, and predisposes Knight to Lacroix's suggestions (it does not make him his mental slave however). His long life also allowed him to master several languages in addition to his native French – Cantonese, English, German, Italian, Latin, Mandarin Chinese, Russian, Spanish and Vietnamese.