Rome, 73 B.C. Spartacus (Kirk Douglas), a Thracian slave, is brought from Libya by Lentulus Batiatus (Peter Ustinov), a Roman trader. He is assigned to the Capuan School of Gladiators. There he meets Varinia (Jean Simmons), a beautiful slave from Britain, and they fall in love. When Spartacus training is almost complete, a Roman general, Marcus Crassus (Laurence Olivier), pays a visit to the school with his protege, Glabrus (John Dall). He demands that two gladiators fight to the death and Spartacus is chosen to confront the Ethiopian warrior Draba (Woody Strode). Draba is victorious, but refuses to finish Spartacus off. Draba turns on Crassua who kills him.
Shortly after, Spartacus escapes with his companions and becomes leader of an army of slaves. He fights and wins his first battle against a Roman army led by Glabrus and trains his men in the mountains of Italy, where Varinia and Antoninus (Tony Curtis), Crassus servant, later join them.
After two years of raiding and beating smaller Roman armies, Spartacus decides to leave Italy and hires a pirate, Tigranes (Herbert Lom), to supply him with ships. Meanwhile in Rome, with unrest and discord is growing due to the slave rebellion and pressure on the armies to do something, Crassus is waiting for an occasion to seize power. Gracchus (Charles Laughton), the leader of the Plebeians, and his ally, Julius Caesar (John Gavin), oppose him.
Arriving with his army on the coast, Spartacus discovers that the pirates, bribed by Rome, will not give him any ships. Unable to withdraw, Spartacus and his army discover that they are surrounded by three Roman armies led by Crassus. In the final battle, the slaves, after a fierce struggle, are routed, and slaughtered by the thousands. The few thousand survivors, who include Antoninus and Spartacus, are taken to Rome to be crucified.
Crassus then finds Varinia with her newborn baby on the battlefield and befriends her. He fails in an attempt to seduce her and, out of malice, orders that Spartacus and Antoninus are to engage in a fight to the death and the survivor will be crucified.
After a long and brutal sword fight, Antoninus is defeated, and Spartacus suffers a slow death on the cross with his slave companions beside him. But before Spartacus dies, Varinia, freed through the influence of Gracchus, shows him their son, a free Roman citizen.
