Procles was one of the Heracleidae, a great-great-great-grandson of Heracles, and a son of Aristodemus and Argia. His twin brother was Eurysthenes. Together the two received the land of Lacedaemon after Cresphontes, Temenus and Aristodemus had defeated Tisamenus, the last Achaean king of the Peloponnesus.

Procles married Anaxandra, daughter of Thersander, king of Kleonoe, who was the sister of his sister-in-law Lathria. He was the father of Soos and the grandfather of Eurypon, the figure regarded as founder of the Eurypontid dynasty of the kings of Sparta.

After the death of Aristodemus the Spartans consulted the oracle at Delphi concerning which of his twin sons should rule. The oracle advised them to set up a dual monarchy. Theras, the brother of Argeia, was made regent.

There was still a necessity of designating the elder of the twins. The Spartans chose the one their mother had fed and cleaned first, Eurysthenes. Consequently the Eurypontid line, descended from Procles, was the less senior in status and decision-making.

The title of archēgetēs, or "founding magistrate," was explicitly denied to Eurysthenes and Procles by the later Spartan government, on the grounds that they were not founders of a state but were maintained in their offices by parties of foreigners. The honor was instead granted to their son and grandson, and for this reason the two royal houses came to be called the Agiads and the Eurypontids.

The line descending from Procles ran through his son Soos to his grandson Eurypon (also called Eurytion), who reached such renown that the house, formerly named the Procleidae after Procles, was thereafter named the Eurypontidae after him.

The death of Aristodemus and the events surrounding it provided a basis for later attempts to date the reigns of the first kings of the Eurypontid line. The Return of the Heracleidae was treated as coinciding with the entry into Arcadia, which Eratosthenes placed at 328 years before the first Olympiad of 776 BC, yielding a date of about 1104 BC.

On this reckoning Procles was born around 1104 BC, which would mark the first year of his reign if the regency of Theras is discounted. Pausanias states that the First Messenian War ended in the first year of the 14th Olympiad, dated to 724/723 BC, roughly 379 years after the return of the Heracleidae. Using such markers, with Isaac Newton's estimate that the nine kings averaged about 42 years each, Procles' reign has been estimated at approximately 1104–1062 BC, though the margin of error remains considerable.