Celie, a young girl who lives with her abusive father, her sick mother, and her younger sister Nettie, begins writing letters to God. In her first letters, she details how her father has been sexually abusing her. Celie becomes pregnant twice, and each time her father gives away the children.
A man named Mr. _____ begins courting Nettie. Celie encourages Nettie's marriage to Mr. _____ because Celie fears her father (Pa) will soon turn his sexual attentions toward Nettie. But Mr. _____ does not permit Nettie to marry Mr. _____, instead insisting that Mr. _____ marry Celie, since she is older and a hard-worker. Mr. _____ believes Celie to be ugly, but eventually is convinced to marry her, because he has several children by his previous wife (who was murdered), and Mr. _____ needs someone to take care of them.
Celie marries Mr. _____ and moves in with him. Nettie later escapes Pa and lives with Celie and Mr. _____ for a brief period. But Mr. _____ still has designs on Nettie, and Nettie flees to town, staying with the Reverend Samuel and his wife Corrine, whom Celie once met, briefly. By coincidence, Samuel and Corrine have adopted Olivia and Adam, Celie's two children. Celie believed she recognized Olivia, when she saw her with Corrine in a shop. Nettie promises Celie she will write to her from her new home, but these letters never arrive.
Celie takes care of Mr. _____'s children, whom she considers "rotten" save for Harpo, the oldest, who marries a strong, hard-working woman named Sofia. Harpo becomes upset that he cannot get Sofia to obey him; both Mr. _____ and Celie (at first) recommend that Harpo beat Sofia. But when Celie sees how Harpo's attempts at beating have hurt both Harpo and Sofia, Celie apologizes to Sofia, and the two become friends.
Shug Avery, a lover from Mr. _____'s past, comes to town, sick, and stays with Mr. _____. They strike up their affair once more, with Celie's knowledge. Celie has been fixated on Shug since seeing a picture of her, on a playbill, when Celie was a girl. Celie and Shug become friends and confidantes, and, later, lovers. Shug begins to sing at a bar Harpo has built behind his shack, after Sofia leaves him (she is tired of being beaten and ordered around by Harpo). Celie tells Shug about her father's sexual abuse, and about Mr. _____'s beatings. Shug promises to protect Celie.
Shug and Celie discover that Mr. _____ has been hiding, for years, the letters Nettie has been sending to Celie. Celie reads the letters and discovers that Nettie, upon moving in with Samuel and Corrine, and their two children Olivia and Adam, began studying to be a missionary in Africa. Nettie then traveled with the family to Harlem, in New York City, on to England, and to various cities in Africa, observing the culture and traditions of the people there, before settling in a village of the Olinka people. Nettie works for Samuel and Corrine, aids in the education of Olivia and Adam, and comes to know a girl named Tashi, whose mother, Catherine, does not approve of Tashi being educated in the Western manner. Celie begins writing letters to Nettie rather than to God.
Corrine, it is revealed, believes that Samuel has had an affair with Nettie back in Georgia, and that Adam and Olivia are actually Nettie's children. This is why, Corrine thinks, Olivia and Adam so resemble Nettie. Nettie swears to Corrine that the two children are her sister Celie's, and Samuel corroborates her story, adding that Celie and Nettie's "Pa" is really their stepfather, and that their biological father was lynched, after his dry-goods store became too successful in the eyes of his white neighbors in Georgia.
Back in Georgia, Celie, spurred on by Shug, confronts Mr. _____ for withholding Nettie's letters for so many years. Celie, Shug, Shug's husband Grady (whom she has married in the interim), and Squeak, Harpo's second wife, move to Memphis, where Shug continues her singing career (Shug already has a house there). Celie begins making pants, a business she will continue for the remainder of the novel, and Squeak and Grady fall in love and move away. Sofia, who was arrested years back for attacking the mayor and his wife after they acted disrespectfully to her, has been serving as the mayor's family maid for twelve years. She is finally released to Celie's home toward the end of the novel. Her children, raised by Harpo and Squeak, no longer recognize her.
Meanwhile, the Olinka village is destroyed by British rubber companies, who plow over the Olinkas crops and hunting land, and charge the Olinka rent and a water tax. Dispirited by their inability to save the village, Samuel, Nettie, and the children return to England after Corrine dies of illness.
In England, Samuel and Nettie realize that they are in love, and marry; they tell Olivia and Adam that their biological mother is Celie, and vow to reunite the families in Georgia. After one last trip to Africa, in which Tashi and Adam are married, Tashi, Adam, Olivia, Nettie, and Samuel arrive at Celie's house in Georgia—the house she inherited from her biological father after her stepfather's death—and find Celie's family in good order. Shug, who had run away for a time with a young man name Germaine for a last fling, has come back to live with Celie and be reconciled with Mr. _____; Mr. _____ himself has found religion and apologized to Celie for mistreating her (he has even carved Celie a purple frog, as a form of apology) and Squeak, Sofia, Harpo, and the remainder of the family realize that, although a great deal has happened over the past thirty years, they, as a family, feel younger and more energetic than ever before.