He was the son of King Anaxandridas II. Dorieus was a half-brother to King Cleomenes I and a brother of Leonidas, who later became king and famous as the Spartan commander at the Battle of Thermopylae. Another brother, Cleombrotus, would later become regent of Sparta.
Attempt to establish a colony in Libya
When Cleomenes succeeded King Anaxandridas Dorieus felt that he was more capable than his half-brother and could not tolerate remaining in Sparta under Cleomenes. So he asked to be sent overseas on a mission to found a Spartan colony in North Africa.
In c.515 BC Dorieus and his companions arrived at Cinyps in the Tripolitania region of modern-day Libya. There they established a settlement further west than any other of the Greek colonies in North Africa.
The great maritime power of the western Mediterranean, the Carthaginian Empire, was not pleased to have Greek colonies intruding into its sphere of influence. Three years after the founding of the colony the Carthaginians in alliance with local Libyans expelled the Spartan colonists.
Expedition to Sicily
After returning to Sparta, Dorieus conceived a new plan to lead an expedition of colonists to Sicily. According to Herodotus Dorieus may have participated in the conquest by Croton of the great Greek city of Sybaris in Southern Italy (510 BC) while on his way to Sicily.
The Spartans landed in Sicily and attempted to found a settlement at a place called Heracleia in the western part of the island near Eryx. However, an alliance of the Carthaginians and Segestans opposed the enterprise and defeated Dorieus and his forces in a battle. Dorieus and most of the leading figures of his expedition were killed.
Herodotus points out that if Dorieus had remained in Sparta and had endured living under the kingship of Cleomenes, he would have eventually succeeded him as king of Sparta as Cleomenes had no sons. Instead it was Dorieus' younger brother Leonidas who succeeded Cleomenes as king and assumed the mantle of an heroic figure by his deeds in the Persian Wars.
- Herodotus Histories 5.42–48