The novel's narrator and protagonist, Hazel is a sixteen-year-old girl living with terminal thyroid cancer that has spread to her lungs. Largely homebound and dependent on an oxygen tank named "Philip," she is deeply concerned about the emotional impact her eventual death will have on her parents.

A charismatic and confident seventeen-year-old osteosarcoma survivor who meets Hazel at a cancer support group. Having lost his right leg to the disease, he is drawn to Hazel’s wit and uses metaphors to express his desire to leave a lasting legacy.

A mutual friend of Hazel and Augustus who has one glass eye and is facing surgery to remove his remaining eye. Despite his cynicism and anger toward his impending blindness, he remains a loyal friend who bonds with Hazel and Gus over video games.

Hazel’s mother and primary caregiver, who dedicates her life to managing Hazel’s medical needs and ensuring she stays active. She is fiercely protective and acts as the emotional anchor for the family.

The earnest and overly optimistic leader of the cancer support group held in a church basement. A survivor himself, he tries to inspire the teens with religious sentiments, though Hazel and her friends often find his methods cheesy.

The reclusive author of Hazel’s favorite book, An Imperial Affliction, who resides in Amsterdam. He holds a mythic status in Hazel's mind for his realistic depiction of dying and becomes central to her quest for answers about the book's ending.

Isaac’s girlfriend at the beginning of the novel who appears very affectionate. She constantly reassures Isaac of her love as he prepares for his eye surgery.

Hazel’s father, who is loving but often emotionally overwhelmed by his daughter's illness. He works during the day and is prone to crying openly about Hazel's condition, contrasting with his wife's more stoic management.

One of Hazel’s few remaining friends from her school days, described as popular and fashionable. She tries to include Hazel in normal teenage activities like shopping, though their different life experiences create a sense of distance.

Peter Van Houten’s personal assistant who manages his correspondence. She serves as a kind bridge between the teenagers and the reclusive author, facilitating their communications.