The play is set in Europe during the Thirty Years' War. Mother Courage, a canteen woman, pulls her cart with her three children (Eilif, Kattrin, and Swiss Cheese) in the wake of the army, trading with the soldiers and attempting to make profit from the war.
We are first introduced to a Recruiting Officer and a Sergeant, who complain about the difficulty of recruiting soldiers for the war. Mother Courage's cart is pulled on and, distracting her with the promise of a transaction, the Recruiting Officer leads Eilif off. One of her children is now gone.
Two years later, we find Mother Courage haggling with the General's Cook over a capon. On the other side of the stage, Eilif is praised by the General for heroically slaughtering some peasants and stealing their cattle. Eilif sings "The Song of the Girl and the Soldier," and his mother joins in. She then berates him for risking his life so stupidly.
Three years later, Swiss Cheese has taken a job as the regiment's paymaster. Yvette Pottier, the camp prostitute, sings "The Song of Fraternization" to warn Kattrin about the horrors of a relationship with a soldier. The Cook and the Chaplain arrive to greet Mother Courage with a message from Eilif, and there is suddenly a Catholic attack. The Chaplain discards his robes, and Swiss Cheese hides the regiment's paybox.
Later the same evening, Swiss Cheese is followed when he attempts to return the paybox to his General but is captured. Mother Courage mortgages her cart to Yvette and tries to bargain with the soldiers using the money--but she bargains for too long, and Swiss Cheese is shot. Mother Courage denies his body when it is brought to her to be identified, so it is thrown into a pit.
The next scene finds Mother Courage waiting to complain outside the Captain's tent. She sings the "Song of the Great Capitulation" to a young soldier who also has come to complain to the Captain. The song, which has the moral "everyone gives in sooner or later," leads to the soldier's storming out, and Courage herself ends up deciding that she doesn't want to complain.
On the day of the funeral of General Tilly, Mother Courage undertakes a stock check, and she talks at length with the Chaplain about whether or not the war will continue. He convinces her that it will, so she decides to invest in more stock for her cart. The Chaplain suggests that Mother Courage could marry him, but he is rejected. Kattrin appears and returns to her mother, severely disfigured, having collected some merchandise. Mother Courage thus curses the war.
In the following brief scene, Courage sings a song that praises the war as a good provider. Business is good for now.
Two peasants wake up Mother Courage, trying to sell her some bedding, shortly before the news breaks that peace has broken out. The Cook returns, unpaid by the regiment, and he instigates an argument between Mother Courage and the Chaplain. Yvette makes her second appearance, now a rich widow, much older and fatter, and reveals that the Cook was once her lover. Mother Courage leaves for the town, and Eilif is dragged along by soldiers. Again he has slaughtered some peasants and stolen their cattle, but it is now peacetime. He is executed for it, but his mother never finds out. She returns with the news that the war is back on again, and she now returns to business with the Cook in tow.
The seventeenth year of the war finds the world in a bleak condition, with nothing to trade and nothing to eat. The Cook inherits an inn in Utrecht and invites Mother Courage to run it with him, but he refuses to take Kattrin. Mother Courage is forced to turn him down, so the two go their separate ways. Pulling the wagon by themselves, Mother Courage and Kattrin hear an anonymous voice singing about the pleasure of having plenty.
The Catholics are besieging the Protestant town of Halle, and Mother Courage is away in the town, trading. Sleeping outside a peasant family's house, Kattrin is woken by their search party, who take one of the peasants with them as a guide. The peasant couple prays for the safety of those in the town, but Kattrin, unseen, gets a drum from the cart and climbs onto the roof. She beats the drum to try to awake the townspeople so that the siege can be anticipated. The soldiers return and shoot her, but before she dies, she is successful in awakening the town.
The next morning, Mother Courage sings a lullaby over her daughter's corpse, pays the peasants to bury her, and harnesses herself, alone, to the cart. The cart rolls back into action, but it is easier to pull now, since there is so little left in it to sell.