Two siblings, Rajasekharan and Radha, become orphans when they lose their mother at a young age. Things take a turn when Rajasekharan's friend Anand falls in love with Radha.

Madhavan marries Thangam. He takes care of Thangam’s mother and brother along with his younger brother. Meanwhile, Madhavan gives shelter to his father’s mistress and her daughter. The evil ladies allege Thangam for loose morals. The rest of the story is how they come into good terms.

Rajan loses his luggage in the train and ends up as a driver in Dharmalingam's family. He falls in love with Gomathy, the eldest daughter of Mullaivaasal Zamindar, his family's arch-rival.

Kathavarayan is rejected by celestial girl named Ilankanni, but he tries to make her fall in love with him anyway.

Poori (Daisy Irani) does not know who his parents are, and has been looking high and low to get back to them. Seated in a park bench beside Sundararajan (Gemini Ganesan), Poori asks his name and as soon as he replies, he proclaims that Sundararajan is his father. This creates complications in Sundararajan’s life and ruins his plans of marrying his lover Latha (Savithri). The president of a hospital for the mentally ill with a not-so-mentally-strong daughter creates more problems for the hero. After many interesting twists and turns, the truth emerges — Poori is the illegitimate child of a soldier (Mustafa) and the abandoned mother commits suicide, leaving the child behind. Sundararajan ro and Latha are so attracted to Poori that they decide to adopt him.

One day, a landlord belonging to a rich family gets murdered and the crime is imposed on Anandar, his innocent brother, and his lovely wife Karpagavalli.

Based on 'Vishnu Purana', the film deals with the story of Prahlada and his devotion to Lord Vishnu.

Kula Deivam was based on a Bengali film Banga Kora by noted writer Prabhavathi Devi Saraswathi