The play is composed almost entirely of speeches and contains little action since its protagonist is chained and immobile throughout. At the beginning, Kratos (strength), Bia (force), and the smith-god Hephaestus chain the Titan Prometheus to a mountain in the Caucasus, with Hephaestus alone expressing reluctance and pity, and then departing. According to the author, Prometheus is being punished not only for stealing fire, but also for thwarting Zeus's plan to obliterate the human race. This punishment is especially galling since Prometheus was instrumental in Zeus's victory in the Titanomachy.
The Oceanids appear and attempt to comfort Prometheus by conversing with him. Prometheus cryptically tells them that he knows of a potential marriage that would lead to Zeus's downfall. A Titan named Oceanus commiserates with Prometheus and urges him to make peace with Zeus. Prometheus tells the chorus that the gift of fire to mankind was not his only benefaction; in the so-called Catalogue of the Arts (447-506), he reveals that he taught men all the civilizing arts, such as writing, medicine, mathematics, astronomy, metallurgy, architecture, and agriculture.
Prometheus is then visited by Io, a human maiden pursued by a lustful Zeus; the Olympian transformed Io into a cow, and a gadfly sent by Zeus's wife Hera has chased Io all the way from Argos. Prometheus forecasts Io's future travels, telling her that Zeus will eventually end her torment in Egypt, where she will bear a son named Epaphus. He says one of her descendants (an unnamed Heracles), thirteen generations hence, will release him from his own torment.
Finally, Hermes the messenger-god is sent down by the angered Zeus to demand that Prometheus tell him who threatens to overthrow him. Prometheus refuses, and Zeus strikes him with a thunderbolt that plunges Prometheus into the abyss.