The Athens-Piraeus Railway Company (SAP S.A.) first opened the line, between Piraeus and Thiseio, on 27 February 1869.

On 4 February 1885 Lavrion Square-Strofyli railway line opened between Attiki Square and Kifissia.

[2] It was electrified in 1904 and since then, taking into account international standards, it can be considered the first metro line in Greece.

In 1855, Prime Minister Alexandros Mavrokordatos tabled a Bill "on the establishment of a railway from Athens to Piraeus", which was published as Law TZ' in the Government Newspaper on 28 December.

According to the law, the railway was classified as a project of public necessity, in order for the contractor to carry out the necessary land sales.

The following year, in 1868, Pickering commissioned the continuation of the project to the newly founded company "Railways of Athens-Piraeus" (SAP SA).

[vague][6] A few days after the inauguration, on 3 March, the "Aion" newspaper wrote: "The railway has been working regularly since last Friday.

[7] In 1882, the Railways of Attica (SA) were established to create and operate a single line that would connect Athens with Lavrio.

[13] Now the urban railway, which had become known in public opinion as "Electric" (because of the electrification, in contrast to the older steam-powered "Thirio"), connected Piraeus with Kifissia.

It is built to 1,435 mm (4 ft 8+1⁄2 in) standard gauge and is electrified using the 750 V DC, third rail, top contact system, also used by Lines 2 and 3.

From Piraeus the line runs eastwards to Faliro and then north to Moschato, Kallithea, Tavros, Petralona, Thissio, Monastiraki, Omonia, Victoria and Attiki.

From Attiki the line continues north, following the alignment of the old Lavrion Square-Strofyli railway through Patissia, Nea Ionia, Iraklio, Marousi and terminates at Kifissia.

[22][23][24] Since 2008, ISAP S.A., and subsequently STASY S.A., proposed a two-phase northern extension of Line 1 from Kifissia to Agios Stefanos, via Ethniki Odos (Athinon-Lamias) near Ekali, bringing the Dionysos municipality into the Athens Metro catchment area.

[25] Since 2020 the project has been decided to consist of an underground part (including a new underground Kifissia station) and the initial extension until Nea Erythrea, with the stations between Agios Stefanos and Nea Erythrea utilising the Suburban railways of OSE, with a further extension towards Varympompi Junction.

Attiko Metro also announced the possibility of a further extension towards Palaio Faliro, along Amfitheas Avenue, instead of Idreika.

[33][34] When the topographical survey was done it was decided that there would be an underground diversion from the station of Thiseio branching out to 3,5km consisting of 4 stations: Ano Petralona, Plateia Davaki, Lofos Filaretou ending at Stavros Niarchos Foundation Cultural Center near Delta Falirou.

[citation needed] The Souflias plan of April 2009 also included a proposal to extend Line 1 from Faliro to Drapetsona and Amfiali (in Keratsini), with a new underground station for Piraeus.

On 13 January 2025 a 69 year old man fell off the station of Aghios Eleftherios halting the schedules and being found dead by ELAS.

On 1 January 2025 the first train scheduled for 2025 malfunctioned having its doors on one side of the train open while in motion between the stations of Ano Patisia and Perissos this took place just 2 days after another incident where in the station of Moschato the tracks started releasing an alarmingly dense amount of smoke.

Just a month later on 31 January in the same station of Moschato the same event happened in the same fashion with officials stating that it may have been caused by a malfunction, most likely, during the use of the breaks.