Most Line 3 trains start or terminate at Doukissis Plakentias: a through service to the Airport leaves once every 36 minutes, and shares most of the extended route with the Athens Suburban Railway.

[7] The line between Dimotiko Theatro and Doukissis Plakentias is underground, and the shared section with the Athens Suburban Railway towards the Airport is a surface-level median of the A6 and A64 motorways.

On 1 March 2012 a contract was signed between Attiko Metro S.A. and a joint venture for the construction of the extension of Line 3 from Haidari to Piraeus, 7.6 km (4.7 mi) long with six stations.

[16] During the construction of the first section of Line 3, Elliniko Metro considered building stations at Geoponiki (Greek: Γεωπονική) on the extension towards Egaleo between Kerameikos and Eleonas, and Girokomeio (Γηροκομείο) on the planned Marousi branch between Panormou and Faros.

[17] On 1 November 2018, STASY introduced a new timetable that scrapped direct metro services to the airport from the city center, due to the lack of spare parts for the fleet.