The line was inaugurated on 2 May 1896, the year of the millennium (the thousandth anniversary of the arrival of the Magyars),[3] by emperor Franz Joseph.

The National Assembly accepted the metro plan in 1870, and the local Hungarian subsidiary company of the Siemens & Halske AG was commissioned for the construction, starting in 1894.

As a result, the infrastructure of the tunnel (the masonry, the load-bearing steel structures, the water insulation, the railway tracks, the architecture of the stations) hadn’t changed at all or very little.

From the middle of the 1980s, they started to show their age, and the serious damage and wear and tear prompted the necessity and urgency of a reconstruction.

[citation needed] As part of a new luxury development project at the Rákosrendező railway station, known as "Millenium City Center" or "Maxi-Dubai", the M1 line would be extended north from the current terminus at Mexikói út to provide better transportation links to the new site.

It would serve brand-new apartments, office buildings, commercial properties, and what János Lázár, Hungary's Minister of Construction and Investment, labeled "Budapest's largest and most modern public park."

It would also include a renovation of the existing railway station as well as a new pedestrian & cycle path to make it easier to access the new development center.

The line opened with 20 electrically powered motor cars built by the Hungarian subsidiary of Siemens and Halske.

One of the original wood panelled cars is maintained in working order and is occasionally used on special services.

One of each of the metal and wood panelled cars, and one of the trailers, are exhibited in the Underground Railway Museum [hu], itself fashioned from the original Deák Ferenc tér station.

The loading gauge constraints of the line meant that all electrical subsystems are fitted above the articulations, between the separate passenger compartments.