With a capacity of 20,000 seats approximately, it counts among the largest ancient theatres in Greece. Nestling in the southeastern side of the castle hill, so as to be linked to the agora, it overlooked the ancient city and was visible from the Argolic gulf. Preexisting small sanctuaries interspersed on the same spot, including those of the Dioskouroi and Zeus Eubouleus, remained untouched during construction of the monument. Built during the Hellenistic period, in the early third century BC, it replaced the oldest theatre of the town, which lied about 100m to the south and was built in the fifth century BC, probably in order to host music and drama contests during the Panhellenic Nemean games, which were then transferred definitively to the town of Argos from the sanctuary of Zeus in Nemea; almost simultaneously, the Heraian games were also transferred to Argos. According to evidence, the oldest Nemean competition taking place in the theatre of Argos in 205 BC involved guitar players and singers. The monument also hosted political conferences, such as the regular Sessions of the Achaian Sympoliteia (League) during the second century BC.
The huge cavea of the theatre, for the greatest part hewn from the rock, is divided by two diazomata (landings) into three horizontal sections and by staircases into four cunei, corresponding to the tribes of Argos. The central section contains 83 rows of seats carved into the rock; additional tiers on both sides are fixed on artificial dykes retained by isodomic walls of unequal measure. Initially circular (26m in diameter), the orchestra was also to the largest part hewn from the rock; its centre featured two embossed reliefs, a circle and two tangent lines for the guidance of the chorus: a circular movement for the dithyrambs and a straight movement in tragedies and comedies. The ?Charonian stairway?, an underground passage that linked the orchestra to the locker rooms, facilitated the appearance of the dead and the chthonic deities during performances. The initial scenic building was built of elaborate limestone. It consisted of the proscenium or front of scene (24.40 x 2.50m), internally decorated with an Ionic colonnade, of the scene above the locker rooms situated on ground level, and of a portico with a Doric colonnade at the front (24 x 5.60m).
The monument was remodelled during the Roman period (second century AD, in particular), in the reign of Emperor Hadrian. It hence hosted various celebrations (Sebasteia festivals, celebrations introduced by Titus, Trajan games, Antinoian games), as well as mock hunts of wild animals or gladiatorial combat; this resulted in the transformation of both the orchestra and the scene. In the first half of the second century BC, the brick scenic building extended to the west, covering part of the orchestra. The proscenium was changed into a two-storey logeio (platform) with marble overlays, adorned with Corinthian colonnades, mosaics and statues in niches. A buckram covered part of the cavea for the protection of spectators from the sun; for their safety during recreations, a net was placed in front of the proedria (seats of honour); both were pitched in rock cavities. In the third century AD was added a tribune with three marble seats for distinguished spectators, such as the representative of the Emperor or the organizing entertainers, and in the fourth century AD, the orchestra acquired an artificial lake for water sports and mock naval battles. The theatre was definitively abandoned in the late fourth century AD.
The monument remained visible for the next centuries, mentioned by almost all travellers and often presented in drawings. It was re-used on the 15th of July 1829, during the 4th National Assembly of the modern Greek state organized by I.Kapodistrias. Excavations were conducted by the French School at Athens in the following years: 1890, 1930, 1954-56, 1981-82 and 1986-87, while 2004 was the year of completion for fixing, restoration and conservation. Today, the theatre houses occasionally a variety of cultural events.