Shivaiah (Kamal Haasan), an autistic orphan, lives along with his grandmother (Nirmalamma) in a village. In that village Lalitha (Raadhika), a young widow with a 5-year-old son, lives along with her brother Chalapati's (Sarath Babu) family. She and her son often get abused by her sister-in-law (Y. Vijaya), but Lalitha, having nowhere to go, bears it all.

Shivaiah often encounters Lalitha and gets appalled by her condition. One day, during Sri Rama Navami festival, Shivaiah marries Lalitha, shocking all the villagers. His grandmother approves of his marriage as she also has much sympathy and regard for Lalitha, but his uncle and Orthodox villagers oppose that marriage as they consider remarriage of a widow was a sin. In that brawl, Shivaiah's grandmother dies leaving innocent Shivaiah in the hands of Lalitha. Lalitha moves in with her husband with the blessings of her brother.

Some of the villagers help them to build a new life. Gradually, Lalitha makes Shivaiah understand the household duties and responsibilities of a man. Shivaiah finds work and starts to support his wife and stepson. Later they have a son and live happily for a long time. Years pass and Lalitha becomes ill and dies in her husband's arms. In the climax, Shivaiah walks out of his house surrounded by his children and grandchildren. He carries a tulsi plant which was his memory of Lalitha's love.

Arun Kumar, and Venkatesh were the production designers for the film.^[8][5] The film was shot for nearly 70 days near the shores of Rajamundry, Torredu, Tadikonda, Pattiseema, Chennai and Mysore.^[8][5] Allu Arjun did a small role of one of the grandsons of Kamal Haasan.^[11]

The scene where Kamal pretends to dance like someone who does not know to dance, took so many days to get it rightly wrong.^[12]

All music composed by Ilayaraja.

Baradwaj Rangan said in 2017, "K Viswanath, this year’s recipient of the Dadasaheb Phalke Award, made three films with Kamal Haasan. Sagara Sangamam is the best, Subha Sankalpam the weakest – and between these two films, chronologically and quality-wise, lies Swathi Muthyam (White Pearl)."^[13]