Candide is a young man who lives in the Barony of Thunder-ten-tronckh. There, he is instructed by the philosopher Pangloss, whose doctrine is that we live in “the best of all possible worlds.” One day, the Baron's daughter Cunégonde comes across Pangloss having sex with Paquette, her mother's chambermaid. Inspired, she approaches Candide, intending to do the same. Unfortunately, the two are caught kissing. Furious, the Baron kicks Candide out of Thunder-ten-tronckh. Candide wanders from place to place, and is eventually tricked by two Bulgarian soldiers into joining their army. He performs well in military exercises, but flees like a coward in the first battle.
Candide makes his way to Holland, because he has heard it is a rich country. There, he begs for money, generally without success. The wife of a Protestant orator dumps a chamber pot over his head after he refuses to say that the Pope is the Antichrist. Eventually, he is taken in by the altruistic Anabaptist Jacques. Shortly thereafter, he comes across Pangloss, who is ill with syphilis. Jacques takes Pangloss in, and also pays for his cure. Pangloss loses an eye and an ear to the disease, but survives. The three travel to Lisbon, debating philosophically on the voyage there.
As soon as they reach the Bay of Lisbon, there is a terrible storm. The ship sinks, and Jacques the Anabaptist dies. Pangloss and Candide float to shore, but as soon as they land, the terrible Lisbon Earthquake takes place, killing thousands. Candide and Pangloss survive, but are soon after arrested by the Inquisition, which is holding an auto-da-fé (a public festival for the punishment of heretics) in an attempt to prevent future earthquakes. Candide is publicly whipped, and Pangloss is hung. Candide despairs, beginning to doubt Pangloss’s optimistic philosophy.
An old woman approaches Candide and leads him to a house in the country. There, he is reunited with Cunégonde, who is being sexually shared by the Grand Inquisitor and a Jewish merchant named Don Issachar. Don Issachar and the Grand Inquisitor both enter the house shortly thereafter, and Candide kills each one as he enters.
Candide, Cunégonde, and the old woman flee all the way to Buenos Aires in South America, where Candide is put in charge of a military company mustered for the war against the rebelling Jesuits in Paraguay. The Governor, Don Fernando, wants to keep Cunégonde as his mistress. News arrives that the minions of the murdered Inquisitor are about to land in Buenos Aires, and Candide flees with his valet Cacambo.
Cacambo takes Candide to the Kingdom of the Jesuits, where he discovers that the Reverend Commandant is none other than the young Baron of Thunder-ten-tronckh. Their tearful reunion takes an unexpected turn when Candide announces his intention to marry Cunégonde, the Baron's sister. Outraged, the Baron attacks Candide, who stabs him through the stomach in self-defense. Candide weeps, overcome with remorse for having now killed three men.
Candide and Cacambo flee the Jesuit Kingdom and head for the wilderness. There, a mishap results in their capture by the savage Oreillons, who take them for Jesuits and prepare to eat them. Thanks to Cacambo's charisma, the Oreillons release them.
Candide and Cacambo wander through the wilderness for a long period of time. Totally by accident, they reach El Dorado, a utopian society filled with precious metals and happy people. Candide concludes that this must be the “best of all possible worlds,” which Pangloss described. Though they are happy in El Dorado, a desire for fame and glory causes Candide and Cacambo to leave. The King of El Dorado helps them depart from the isolated place, giving them many riches and a flock of red sheep as a parting gift. A few days after leaving El Dorado, Candide and Cacambo come across an African slave who is missing his hand and left leg.
Knowing that he will be arrested if he returns to Buenos Aires, Candide sends Cacambo to search for Cunégonde, promising to meet him in Venice. Candide himself heads to Suriname, where he tries to arrange passage back to Europe. He is tricked by the ship owner Mynheer Vanderdendur, who steals his flock of sheep and abandons him. At this point, Candide is almost ready to abandon his optimism completely.
Nevertheless, Candide manages to arrange a journey to Bordeaux with Martin, an impoverished scholar and pessimist whom he chooses as his traveling companion. On the way there, a battle takes place between two ships, and one of Candide's red sheep floats up from the wreckage, alive—he takes this as a good omen.
Candide and Martin arrive in Bordeaux, and then head to Paris. In Paris, Candide is tricked and robbed by the devious and superficial Abbé of Perigord and Marchioness of Parolignac, along with many other minor characters.
Candide and Martin briefly go to England, and then move on to Venice. There, Candide finds Paquette in the arms of Friar Giroflée—she has become a prostitute. Candide and Martin visit the home of Pococuranté, a wealthy Venetian Senator who is dissatisfied with everything he has. Soon after, they have dinner with six kings who have been deposed. At the dinner, Candide finds Cacambo, who informs him that Cunégonde is working as a servant in Turkey.
Candide, Cacambo and Martin travel to Turkey. On the ship which takes them there, they find Pangloss and the Young Baron, both of whom have been enslaved. Candide pays to have them both freed. When he arrives in Turkey, he does the same for Cunégonde and the old woman. By now, after lengthy journeys and countless misfortunes, all of the major characters have been reunited.
Cunégonde has become ugly, but Candide still wishes to marry her. When the Baron, her brother, opposes it, they send him back to Rome—by force. The two marry, and all of the remaining characters move to a small farm. There, they complain about their misfortunes and discuss philosophy endlessly.
One day, Candide comes across an old Turkish farmer, with a garden he takes care of with his children. The man seems to be happier with his lot than Candide and the other characters. Because of him, Candide is inspired to abandon the endless questions of philosophy for the solace of practical work. He concludes that while we are alive, “we must cultivate our garden.”