He was the son of Eëtion and a disfigured woman named Labda, a member of the Bacchiad family, the ruling dynasty of Corinth. According to Herodotus the Bacchiadae heard two prophecies from the Delphic oracle that the son of Eëtion would overthrow their dynasty, and they planned to kill the baby once it was born. However, Herodotus says that the newborn smiled at each of the men sent to kill it, and none of them could go through with the plan. Labda then hid the baby in a chest, and when the men had composed themselves and returned to kill it, they could not find it. The baby was named Cypselus after the Greek word for "chest," cypsele.
When Cypselus had grown up, he fulfilled the prophecy. Corinth had been involved in wars with Argos and Corcyra and the Corinthians were unhappy with their rulers. At the time, around 657 BC, Cypselus was polemarch, the archon in charge of the military, and he used his influence to expel the king. He also expelled his other enemies, but allowed them to set up colonies in northwestern Greece. He also increased trade with the colonies in Italy and Sicily. He was a popular ruler, and unlike many later tyrants, he did not need a bodyguard and died a natural death.
He ruled for thirty years and was succeeded as tyrant by his son Periander in 627 BC. The treasury Cypselus built at Delphi was apparently still standing in the time of Herodotus.