Thorikos was an ancient deme — a local administrative community — on the southern tip of the Attica peninsula, just north of what is now Lavrio and not far from the silver mines of Laurion. The theatre sits on the southern slope of a hill called Velatoúri, carved from local limestone quarried nearby. Its setting is industrial as much as cultural: the same landscape that produced the silver that built Athens' fleet contained this, one of the earliest civic gathering spaces in the ancient world.

The theatre was not designed for drama alone. It functioned as a meeting place where citizens of Thorikos gathered for civic purposes — assemblies, religious festivals, public business. The distinction between theatre and civic forum was, at this early stage, not yet firmly drawn.

The theatre was built in phases across roughly two centuries. In the first phase of construction, there were approximately 19 to 21 straight rows of stone benches, divided by two vertical staircases into three sections of unequal width. The middle section's benches run at a slight diagonal — another sign of pragmatic construction rather than geometric idealism.

In the mid-5th century BCE, curved sections were added to both ends of the original straight gallery. In the 4th century BCE, further curved rows were added at the rear, probably including some wooden benches. Two entrances on the north side gave access from outside to the upper seating area; a raised walkway led from the slope on the west. At its largest, the theatre could hold between 2,000 and 3,200 spectators — a substantial audience for a community built in the shadow of the mining works.

Despite holding the distinction of being the oldest known stone theatre in the world, the Theatre of Thorikos is not a famous destination. It lies outside the major archaeological tourism circuit of southern Attica, which tends to begin and end with the Temple of Poseidon at Cape Sounion. The site is largely unrestored; the benches sit as they were found, weathered and worn, in a working archaeological landscape rather than a curated monument.

American scholars from the School of Classical Studies at Athens reported on the theatre as early as 1885–1886. Belgian teams excavated and documented the site extensively through the 1960s onward, publishing detailed analyses of its geometry and construction phases. The theatre has been the subject of continuing scholarly interest precisely because its irregular form illuminates the process by which Greek theatrical conventions were invented, not received whole.