Part I introduces readers to the main character, the Igbo warrior Okonkwo, who lives in Nigeria in the 1890s. Okonkwo is the son of a lazy debtor, Unoka, who was irresponsible and seemed to never work. Embarrassed by his bad heritage, Okonkwo sets out to become a great man, winning early fame as a wrestler by throwing Amalinze the Cat. On the strength of this fame, he's able to borrow seeds from a man named Nwakibie in order to start a farm. After years of hardship, he's able to pay his debt and become a wealthy farmer with several barns full of yams (a sign of great social status). In the process, he also marries three wives, who bear him many children, including Nwoye, his eldest son, and Ezinma, his favorite, whom he often wishes were a boy.
In recognition of Okonkwo's great wealth and status, he's charged with the care of a prisoner of war, a young boy named Ikemefuna who was sacrificed by his home village of Mbaino so they might avoid war with Umuofia, Okonkwo's clan, after men from Mbaino slaughtered one of the daughters of Umuofia. Unsurprisingly, Ikemefuna is afraid of Okonkwo at first, because the man is curt and violent and often acts rashly, spurred on by his extraordinary arrogance; but with time the boy begins to think of Okonkwo as his father, and though Okonkwo won't show anyone, he feels great affection for his charge. More so than for his own son, whom he considers weak.
One day, Okonkwo's youngest wife goes to her friend's house to plait her hair and doesn't return in time to make the afternoon meal. Okonkwo beats her, but because it is the Week of Peace, he's punished for this, because his tribesmen fear that his actions will anger the earth goddess Ani and lead to trouble in Umuofia. He's required to repent by giving a tribute to the goddess. Soon after, during the Feast of the New Yam, Okonkwo is again driven to anger by his youngest wife when, after witnessing his poor shooting, she makes a snide remark about his pistol, of which he's very proud. He shoots at her, but misses. The Feast continues, and Okonkwo and his wives all enjoy watching the ceremonial wrestling matches.
Locusts appear in the village. They appear to be a good omen, at first. People roast the locusts to eat as a delicacy, but their arrival portends the death of Ikemefuna, which has been decreed by an Oracle. Okonkwo and several men from Umuofia agree to lead Ikemefuna away from the village on the pretense of taking him back to Mbaino. On the way, the men try to kill Ikemefuna. Scared, the boy turns to Okonkwo, calling him father, but Okonkwo strikes him down, afraid of seeming weak. He's understandably upset by this, and the elders question his actions. He's able to help his friend Obierika negotiate his daughter's bride price, but soon after, Ezinma grows gravely ill, and a medicine man must be called to heal her. This contributes to Okonkwo's downward spiral.
Following incidents where the fate of an abused wife is determined by Umuofia's spirit ancestors and Okonkwo's daughter Ezinma is roused from her sleep by Chielo, the priestess of Agbala, the village gathers to celebrate the day of Obierika's daughter's uri, when her suitor brings palm wine for her parents and the other villagers. The joyous occasion is immediately followed by a somber one: the funeral of Ogbuefi Ezeudu, the oldest man in their village. During the funeral, guns are fired in Ezeudu's honor. Okonkwo's gun, however, explodes, and the shrapnel pierces the heart of Ezeudu's son and kills him. Okonkwo is subsequently banished to his mother's village of Mbanta for seven years.
In his mother's village of Mbanta, Okonkwo is given some land and yam seeds in order to build a new farm and compound. He's well received in the village, but he falls into despair, so one of the elders has to explain to him that his suffering isn't nearly so terrible as those who are exiled from their villages forever or who bear sets of twins, who are left to die in the Evil Forest, because the villagers think that twins are like demons. In his second year of exile, his friend Obierika comes to visit, bringing him stories of how white men on "iron horses" (bicycles) came to their village, and because the Oracle said the white men were evil locusts come to destroy them, the villagers killed the white man, and the man's friends killed one of the villagers, a man named Abame. The visit ends with Obierika giving Okonkwo some of the money from the sale of his yams and yam seeds, which would have rotted in Umuofia had Obierika not sold them.
Two years later, Obierika again visits Okonkwo, this time to talk about his eldest son, Nwoye, who has joined the Christian missionaries. Okonkwo had disowned Nwoye because of this and had grown to hate the missionaries intensely, because they offended the Igbo gods. He and some of the other men in the village had given the missionaries part of the Evil Forest to build a church and some huts, thinking that the Evil Forest would destroy them, but the missionaries were never harmed by the gods, and they were able to convert Nwoye to their cause. However, when one of the missionaries kills a sacred python, tensions between the two groups heighten, and the men of the village consider taking action against the missionaries. Then, when the man supposed to have killed the python takes ill and dies, the villagers think the gods have spoken and decide to let the missionaries off the hook. Soon after, Okonkwo invites the great men of Mbanta to an enormous feast. This ends Part II.
Part III opens with Okonkwo planning a glorious return to Umuofia. He has convinced Ezinma, who has been dubbed the "Crystal of Beauty" in Mbanta, to refuse offers of marriage until their family returns to Umuofia. However, when the exile ends, Okonkwo is disappointed to learn the missionaries have built a church in his village, where white men have imposed their foreign form of government on the villagers. Mr. Brown, a kind Christian man who preached compromise and peace with the villagers, is replaced by Mr. Smith, who takes a more aggressive approach. Upset by the changes that have taken place in Umuofia, Okonkwo leads a group of men in burning the white man's church to the ground. He and the men are subsequently arrested and humiliated by a group of court messengers, who demand payment to set the warriors free.
Without the support of the villagers, Okonkwo decides to take matters into his own hands. After he kills the head messenger, he hangs himself in his compound. Suicide is an abomination in his culture, and the men in his village are not allowed to cut him down or even to touch his body. A white man has to cut him down under orders from the District Commissioner, who arrived at the compound intended to arrest Okonkwo. The Commissioner then leaves, thinking of the book that he'll write about this country and of the interesting paragraph that Okonkwo's story will make.