Ancient authors disagree on Phineus's parentage. Apollonius of Rhodes makes him a son of Agenor; Apollodorus notes that others named Poseidon as his father. The Hesiodic Catalogue of Women instead reports Phoenix and Cassiopeia.

His first wife is commonly Cleopatra, daughter of Boreas and Oreithyia, by whom he had a pair of sons whose names vary widely in the sources (among them Plexippus and Pandion). A second wife — often Idaea, daughter of a Scythian king — is said to have deceived him into blinding those sons. By a later partner he is also credited with sons such as Mariandynus and Thynus, eponyms of neighbouring peoples.

Apollo was said to have given Phineus the gift of prophecy. Reasons for his own blinding and torment differ: revealing the gods' secrets to mortals (the best-known Argonautica version), choosing long life over sight, punishing his sons at a stepmother's urging, aiding Phrixus, or offending Helios or Poseidon. In the central tradition the Harpies snatch or foul every meal laid before him.

When the Argo reaches his Thracian home, Phineus explains that his brothers-in-law Zetes and Calais are fated to deliver him. The Boreads pursue the Harpies to the Floating Islands; Iris stops the chase and swears by the Styx that the Harpies will trouble him no more. In return Phineus prophesies the voyage ahead and teaches the crew how to pass the Symplegades — releasing a dove so that they may time their rush between the Clashing Rocks.

Aeschylus wrote a now-lost play Phineus; Sophocles' Antigone alludes to the Cleopatra episode. Later anecdote has Helios transform Phineus into a mole, a blind creature, for some insult.

Greek myth knows more than one Phineus. The Ethiopian brother of Cepheus and rival of Perseus for Andromeda is a separate figure treated under `phineus-ethiopia`. This notice concerns only the Salmydessian seer of the Argonaut saga.