Sivaji Ganesan portrays three roles: an insecure father, a timid son and an angst-ridden twin brother. Sivaji Ganesan, a lawyer with a scarred face, gets married to Pandari Bai. The couple lead a happy life and Pandari Bai gives birth to twin brothers, a son with a scarred face (Also Ganesan) like his father and a brother (Also Ganesan). Their father unable to tolerate his eldest son's face leaves him under the custody of another person and tells his wife that the first child is dead. As years pass by, the father becomes a justice and his younger son, a happy-go-lucky college-going timid son, falls in love with Jayalalithaa. In the meanwhile, the elder son comes to know about his family and tries to meet his mother and brother but he is asked by his father not to reveal his identity to them. M. N. Nambiar, a man once punished by the father, kidnaps the younger son in order to take revenge on him. In the end, the elder son rescues his brother, killing M. N. Nambiar. He succumbs to his injuries and dies on the lap of his mother (Pandari Bai). This film was the first Tamil film recommended for an Oscar.
Deiva Magan was adapted from Bengali play Ulka by Nihar Ranjan Gupta. G. V. Iyer earlier adapted the play into a film called Thayin Karunai (1965) with Muthuraman which failed at the box office, "Deivamagan" was the second adaptation of the play. Sivaji who was impressed with the plot decided to make the film and made his friend Periyanna to produce the film. The film was initially titled as "Uyiroviyam" before finalising "Deivamagan".
The film involved the characters of father and his two sons which would be tough to be acted by the same person so the director wanted two young actors to play the characters of two sons. However Sivaji accepted the challenge and acted in the role of both sons, bringing a difference in body language and mannerisms to each role.
The film was dubbed in Telugu as Koteeswaralu. The film was remade in Hindi as Bairaag (1976) with Dilip Kumar.
Deiva Thirumagal, a 2011 Tamil film starring Vikram which was earlier titled as Deiva Magan was thought to be the remake of this film, however the director denied it by saying the story of both these films are no way connected with each other and eventually the new film's title was changed as Deiva Thirumagal.
Tamil magazine Ananda Vikatan said in its review, "A film with multiple roles of same actor without any confusion which itself a milestone, Makers have tried to built a hall with just one pillar and that was Sivaji Ganesan!.