Respected among his peers and community, Siddhartha, a young Brahmin, lives a near-perfect life with his best friend, Govinda, in ancient India. Despite his fulfilled religious duties and rituals, Siddhartha feels a void within him. He sees his father and elders failing to attain enlightenment and believes that he will not find the answers to his existential questions by following their path. When a group of austere ascetics, the Samanas, arrive in their town, Siddhartha decides to follow their self-denying teachings, believing that it might provide the answers he seeks. Govinda, too, joins Siddhartha in his new path, despite his father's reluctance.

With his Brahmin upbringing giving him the required patience and discipline, Siddhartha easily adapts to the ways of the Samanas. He learns to renounce worldly pleasures and possessions, aiming to achieve enlightenment by completely negating his Self. Govinda appreciates their new lifestyle and the spiritual progress they've made. However, Siddhartha remains discontented, realizing that even the oldest Samanas haven't attained true enlightenment. Hearing about a new enlightened holy man, Gotama, Siddhartha and Govinda decide to leave the Samanas and seek him out, despite the leader's disapproval.

Siddhartha and Govinda join Gotama's followers, learning his teachings on the Eightfold Path and Buddhism. Govinda becomes a devotee, but Siddhartha sees a contradiction in Gotama's teachings, questioning the concept of embracing the unity of all things while surpassing the physical world. Dejected and convinced Buddhism won't answer his questions, Siddhartha leaves Govinda behind to explore the worldly pleasures. In this pursuit, he meets Kamala, a beautiful courtesan, who lures him into the life of a merchant, where he becomes rich but spiritually empty.

His disillusionment with materialism drives him to leave everything behind and find solace near a river. Encountering Govinda who is now a Buddhist monk, and a humble ferryman, Vasudeva, he begins contemplating the unity of life. Kamala's untimely death due to a snakebite leaves Siddhartha as the single father to their son, who despises their simple life and eventually runs away. With Vasudeva's guidance, Siddhartha learns to find solace in the river's wisdom, understanding the cyclical and interconnected nature of life.

Siddhartha's journey ends when Govinda visits the river seeking enlightenment from an unknown wise man, who is Siddhartha himself. Siddhartha tells Govinda that true wisdom cannot be verbally communicated. He urges Govinda to kiss him on his forehead, and in doing so, Govinda experiences the unity of life that Siddhartha has achieved, thus fulfilling their childhood quest for enlightenment.