Headquartered in the Ellinoroson neighbourhood of the center of Athens, the Greek government created the company in July 1991: Elliniko Metro's original purpose was to oversee the delivery of the Base Project of the Athens Metro, which opened in three stages, in 2000 and 2003.

[2][3] The Base Project consisted of two lines with a total length of 17.6 kilometres (10.9 miles) and 20 stations, and opened in three phases from 28 January 2000 to 22 April 2003.

[6] Law 1955/1991 allows the partial privatisation of Elliniko Metro in the future, but the Greek government must retain a controlling interest of at least 51% over any resultant company: Elliniko Metro may also only merge with mass transit organizations that operate within the area of the former Attica Prefecture.

Elliniko Metro previously had two operational subsidiaries to operate and maintain Metro lines 2 and 3, and the current Athenian tram network: on 17 June 2011, AMEL and Tram S.A. merged with Athens–Piraeus Electric Railways (ISAP) to form STASY, a subsidiary of Transport for Athens (OASA) instead of Elliniko Metro:[10][11][12] The logos of both companies were the same as the system that they operated.

In this table, the completion date refers to the opening of the last section or station in the contract: for example, the initial scheme of the Athens Metro opened in three stages, on 28 January 2000, 15 November 2000, and 22 April 2003.