Piranesi/Matthew Rose Sorensen
The main character and the narrator of the novel, Piranesi is introduced as one of the two surviving people inhabiting a large compound filled with statues that he calls the House. The character of Piranesi is shown as a calm and collected individual, contentedly fulfilling the tasks around the House, enjoying the simple things and small acts of kindness by the Other. Matthew Rose Sorensen is revealed as a science and anthropology enthusiast who decided to write a book about Laurence Arne-Sayles. He mysteriously disappears soon after his decision to pursue this task and interview people close to Arne-Sayles.
The Other/Valentine Ketterley
The Other is described by Piranesi as being the only other living human in the world. He visits him about once a week, sometimes bringing him necessary things like shoes and food. Right from the start, it is clear that Piranesi and the Other live completely different lives. The Other has access to all the necessary things, he seems sharper and more aware than Piranesi, the truth behind which is revealed towards the end. Valentine Ketterley is revealed to be an academic and psychologist who strictly opposes Laurence Arne-Sayles and his insane beliefs and ritualistic endeavors, while secretly trying to find a way to reach the sacred knowledge from the other worlds.
16/Sarah Raphael
The mysterious 16 appears as a potential sixteenth person inhabiting the House/world. The Other warns Piranesi that this person is dangerous and wants to drive him to madness, so he should better stay out of their path. Piranesi agrees, but once he discovers that 16 is a woman, he can't help but communicate with her with messages on the wall. Sarah Raphael is a police officer who decided to investigate the strange and sudden disappearance of Matthew Rose Sorensen. Unlike her colleagues, she has an open mind and decides that the best way to discovery is to listen to Arne-Sayles. Arne-Sayles shows her the way to open the doors to other worlds, behind one of which she will find Rose Sorensen.
