During the construction of the enormous complex of the National Palace of Culture, two stations forming part of the M2 line and their connecting tunnels were built.

Following the ratification of a technical and economic report on the metro by the Council of Ministers of Bulgaria, and the subsequently approved General City Plan, the general scheme for the development of the lines should consist of three diameters with extensions in the periphery, with a total length of 72.5 kilometres (45.0 mi), 75 metro stations, and a 1.1 million daily passenger capacity at the final stage of implementation.

2006 saw the start of the construction of another section of the same line (consisting of 3.2 kilometres (2.0 mi) of tunnels and three stations) linking Izgrev and Mladost I housing estate.

(Сливница) first station of the section, shared with M4 (Люлин) (Западен парк) (Вардар) (Константин Величков) (Опълченска) (Сердика) (СУ „Св.

[17] Construction of the 6.4 km (4.0 mi) section between Nadezhda interchange and Lozenets district via Central railway station and the National Palace of Culture started on 14 December 2008.

[17] NDK and European Union stations and their connecting tunnels were partly completed during the construction of the National Palace of Culture and the redevelopment of the surrounding area in the late 1970s and early 1980s.

The construction of Mladost 3 and Inter Expo Center – Tsarigradsko shose stations began on 15 February 2009 and was completed on 25 April 2012.

The further extension to Sofia Airport comprising two underground and two overground stations and a length of 4.968 kilometres (3.087 mi) began in 2013,[13][18][19][20] and was completed on 2 April 2015 at the cost of BGN 136,757,630 (EUR 69,923,066), VAT exclusive.

Provisions have been made for the construction of future branch to Iliyantsi, starting from the existing junction located between Knyaginya Maria Luiza and Han Kubrat stations.

The split is in preparation to the future construction of the Pancho Vladigerov station, which is supposed to physically separate the lines and will allow them to have independent timetables.

(Обеля) (Ломско шосе) (Бели Дунав) (Надежда) (Хан Кубрат) (Княгиня Мария Луиза) (Централна ж.п.

гара) (Лъвов мост) (Сердика II) (Национален дворец на културата) (Европейски съюз)[21] (Джеймс Баучер) (Витоша) (Обеля) (Панчо Владигеров) (Младост III) (Интер Експо Център – Цариградско шосе) (Дружба) (Искърско шосе) (Софийска Света гора) (Летище София) M5 is a planned line, servicing Studentski grad and Iliyantsi.

The project design contract was awarded to the Czech company Metroprojekt Praha a.s.[23][24][25] In March 2014, a tender for construction of the central section of the line was announced.

Driverless train operation, with Grade of Automation 3 (GoA 3), and platform screen doors will ensure the safety of the passengers.

(Хемус) (Владимир Вазов) (Стадион „Георги Аспарухов") (Хаджи Димитър) (Театрална) (Орлов мост) Future M6 line, heading east, diverges from M3 after this station.|| In Knyazheska gradina park.

Патриарх Евтимий) (Национален дворец на културата II) (Медицински университет) (България) (Красно Село)

The older train sets, type 81-717/714.4, were manufactured by Metrowagonmash in Mytishchi, Moscow Oblast, Russia and consists of 48 carriages in total.

In July 2023, Škoda Transportation won a contract worth 65 million EUR, to deliver 8 four-car air-conditioned metro trains, replacing the current Metrowagonmash.