Sivaji Ganesan, N. T. Rama Rao, Savithri, Devika
Unmarried princess Kunti is blessed by the Sun god with a baby boy, which she abandons in the Ganges to avoid embarrassment. The boy is rescued and adopted by charioteer Athirathan, who names him Karnan. Years later, the now-grown up Karnan realises that Athirathan is only his adoptive father and feels heartbroken. He does not want to become a charioteer like Athirathan, and instead chooses to become a warrior. He masters archery and challenges the Pandava prince Arjuna in a contest. Karnan is insulted on account of his lowly birth, but the Kaurava prince and cousin of the Pandavas, Duryodhana, saves his pride, and gives him the kingdom of Anga. Karnan thus becomes the close friend of Duryodhana and his wife Bhanumati.
One day, Indra, the king of the Devas (celestial deities), disguised as a Brahmin, approaches Karnan and asks for his armour and ear rings in donation to weaken and stop him from overpowering Arjuna. Aware of Indra's intention, Karnan yet donates both the items he was born with and which would make him invincible. Pleased with Karnan's generosity, Indra gives him a powerful weapon, Nagastra, but states that he can use it only once. Karnan, disguised as a Brahmin, becomes the student of the sage Parasurama to acquire the Brahmastra; one day, however, Parasurama realises that Karnan is a Kshattriya, a tribe he opposes. Enraged, he renders Karnan incapable of using the Brahmastra when most needed, and banishes him.
Karnan later saves princess Subhangi from an uncontrolled chariot, and they fall in love. Subhangi's parents initially disapprove of their romance, but eventually they accept, and the couple get married. A few years later, Krishna, a supporter of the Pandavas, learns about Karnan's true background. He tells Kunti that Karnan is her first son whom she abandoned. Karnan gets to know about his birth later. Kunti meets Karnan and gets two wishes from him, one that he will not attack any of her sons (the Pandavas) except Arjuna during the impending Kurukshetra War, and that he will attack Arjuna with the Nagastra weapon only once. Karnan refuses to join his brothers, the Pandavas and remains the friend of their enemy Duryodhana.
Before the start of the Kurukshetra war, Duryodhana’s ministry assembles to appoint the generals of the army. Bheeshma is appointed the Commander and he starts nominating generals for different battalions. Karnan is insulted on account of his lowly birth and given the command of a low rank infantry. The war begins and in the early days, Bheeshma retires and Karnan replaces him. The following day, Karnan goes to war accompanied by his son Vrishasena who fights bravely, but is killed by Arjuna afterwards.
The next day, the vengeful Karnan uses the Nagastra to try killing Arjuna, but Krishna saves Arjuna by preventing the arrow from hurting him. Since Karnan cannot use the Nagastra more than once, he is unable to kill Arjuna. A wheel of his chariot gets stuck in a big hole, and he steps down to relieve it. At that time, Arjuna, under the direction of Krishna, shoots many arrows at Karnan that severely wound him. Krishna tells Arjuna that the Dharma (noble charity) that Karnan performed during his lifetime was protecting his life. Krishna disguises as a Brahmin, goes to Karnan and asks him his virtues as donation. Out of generosity, Karnan donates all his virtues to the "Brahmin". At this juncture, Arjuna shoots a few more arrows at Karnan that kill him. The Pandavas, who realise that Karnan was their eldest brother mourn his death. His mother Kunti also mourns his death, while Subhangi dies due to the trauma of her husband's death in the war. Arjuna remorses killing Karnan, until Krishna reveals that the curses by Indra and Parasurama were also responsible for his death. The film ends with Karnan meeting his father — the Sun in the other world.