Pi Patel, an immigrant from Pondicherry in India living in Montreal, Canada, is approached by a local novelist who has been referred to him by his "uncle" (a family friend), believing that Pi's life story would make a great book. Pi relates an extended tale:

His parents had named him Piscine Molitor after a swimming pool in France. He changes his name to "Pi" (the mathematical symbol, π) when he begins secondary school, even repeating numerous digits of pi, because he is tired of being taunted with the nickname "Pissing Patel". His family owns a local zoo, and Pi takes an interest in the animals, especially a Bengal tiger named Richard Parker because of a clerical error. To teach him the reality of the tiger's nature as a carnivore, Pi's father forces him to witness it killing a goat. He is raised Hindu and vegetarian, but at 12 years old, he is introduced to Christianity and then Islam, and starts to follow all three religions. As an adult he states that he is Catholic-Hindu, and when asked if he is also Jewish, he replies that he lectures in Kabbalah at the university.

When Pi is 16 , his father decides to close the zoo and move his family to Canada, and sell the zoo animals. They book passage with their animals (to be sold in North America) on a Japanese freighter named the Tsimtsum. The ship encounters a heavy storm and begins to sink while Pi is on deck marveling at the storm. He tries to find his family, but a crew member throws him into a lifeboat; from the rough sea, he watches helplessly as the ship sinks, killing his family and its crew.

After the storm, Pi finds himself in the lifeboat with an injured zebra, and is joined by an orangutan who lost her offspring in the shipwreck. A spotted hyena emerges from the tarp covering half of the boat, and kills the zebra. To Pi's distress, the hyena also mortally wounds the orangutan in a fight. Suddenly the tiger Richard Parker emerges from under the tarp, and kills and eats the hyena.