Early life (1979-1990)
Jace was born to Stephen and Céline Herondale in Great Britain in 1979. His early life is unknown.
Hogwarts years (1990-current)
Jace was sorted into Gryffindor during his first year at Hogwarts. He has managed to complete the first three years without much incidents. He has had a crush on August Doww for years now. However, he is uncertain to act on his feelings in fear of being rejected.
Jace is known for and has a strong title for his good looks. He is described as having fine, curly, golden blond hair, long eyelashes, and eyes that look gold in the light, due to the magical experiments performed on him and the angel blood in his veins. He has a slim, muscular build and is about 5'11" in height.
His face is often described as being beautiful, sexy, gorgeous and angular and Clary often refers to him as beautiful and leonine, with a narrow mouth. Like all other Shadowhunters, he is covered in thin, silver scars from years of applying various magical runes with a stele for battle and healing purposes, as well as permanent runes that look like tattoos.
The only flaw in his face, as Clary has noticed, is the slight chip in his incisor teeth. Clary is said to be relieved by this as it is a proof that he is not that inhumanly handsome and perfect. It is said that Jace is seventeen years old, though that was assuming he was Valentine (or Michael Wayland's) son, and his real age is determined to be between a few years younger than Jonathan Christopher and a year or so older than Clary. After "doing the math" by looking through the things of his father Stephen's, and the time the Uprising occurred, he discovered that he was born in January, and is six months older than Clary.
Jace is also noted to be left-handed (like Valentine). He is said to look like his true father, Stephen Herondale, except around the eyes where he looks like his mother, Céline Herondale.
He has a star-shaped birthmark on his left shoulder.
Personality and traits
Jace had always been independent and somehow self-possessed, having been taught not to betray himself to emotions as a child.
Jace has a sharp, defensive wit, an acidic temperament, and a very sarcastic attitude when he chooses. Giving the impression of holding most people in disdain, Jace is seen as extremely arrogant, self-centered, and overconfident, believing himself to be "the best Shadowhunter to ever live" and above others. True enough, Jace is superior in battle, something Jace has been training for since he was young and had grown to love over the years. He even exhibits sadistic tendencies, which he got on account of being raised by Valentine.
Despite this, Jace in fact has a strong moral core. He is dutiful and just, willing to make the right decisions, and sacrifices if it comes down to it. Though he can be, at times, vindictive, he is cruel only to protect those he loves.
His conceited exterior hides a profound inner hatred which intensifies after he mistakenly believed he was demonic, blaming the demon blood for his conflicting thoughts and his, then presumed, incestuous feelings towards Clary. Even after this was disproved and contradicted by the fact that he actually is actually part angel, even more so than regular people of his kind, Jace continued to carry the weight of the lies he had lived for so long. An example of this is Jace's love for the man who raised him and whom he believed to be his father, Valentine; despite the abuse and the deceit, Valentine was at times kind and affectionate towards him, and Jace found himself missing his father figure.
Like Valentine and the Lightwoods, Jace also shared the snobbish attitude toward mundanes and Downworlders, though he lacked their extremist tendencies. Beneath Jace's flippant exterior lies a soul in constant torment, filled with a deep-seated rage that he keeps in check most of the time and channels into fighting and slaying demons and also, sometimes, his sarcastic and nasty remarks. Jace relaxes and calms his nerves by getting into fights, with Clary even noting that fighting to Jace is "what sex is to normal people."
Aware of his own beauty, Jace was also once quite chivalrous, and quite flirty, towards women before he met Clary. His charisma, good looks, and charm have made him quite the ladies' man. However, taught that "to love is to destroy" at an early age, Jace kept everyone, except the Lightwoods, at arm's length, never forming emotional attachments for more than a brief amount of time, if at all. His personality drastically changed after he met Clary, with Isabelle even stating that Jace was apathetic about everyone else beforehand, not caring about anyone other than the Lightwoods until he met Clary, whose presence shook Jace, who was revealed to be a very passionate individual, loving Clary on a very deep and passionate level when he fell in love with her and does everything in his power to protect her from harm, the extent of his love for Clary even surprising those close to him.