In the September 1919 session of the Imperial Legislative Council at Shimla, a committee was set up by W. E. Crum that recommended a metro line for Kolkata (formerly Calcutta).

[5] This line was supposed to connect Bagmari in the east to Benaras Road, Salkia, in Howrah in the west via a tunnel beneath Hooghly River.

The estimated construction costs were £3,526,154, about ₹36.4 crore (equivalent to ₹70 billion or US$810 million in 2023) based on current exchange rates, and the proposed deadline was 1925–1926.

[7][5][8] Then the Chief Minister of West Bengal, Bidhan Chandra Roy, reconceived the idea of an underground railway for Kolkata from 1949 to 1950.

The MTP, with the help of Soviet specialists, Lenmetroproekt and East German engineers, prepared a master plan to provide five rapid-transit (metro) lines for the city of Kolkata, totaling a length of 97.5 km (60.6 mi), in 1971.

[11][13] The foundation stone of the project was laid by Indira Gandhi, the Prime Minister of India, on 29 December 1972, and construction work started in 1973–74.

Initially, cut and cover along with slurry wall construction to handle soft ground, was recommended by the Soviet Union consultants.

From the start of construction, the project had to contend with several problems including insufficient funds (until 1977–1978), a shifting of underground utilities, court injunctions, and an irregular supply of vital materials.

[15] The Blue Line was almost entirely built by cut and cover method, while a small 1.09 km stretch between Belgachia and Shyambazar was built using shield tunneling with compressed air and air locks, since the alignment crossed a railway yard (now Kolkata railway station) and Circular Canal.

[20] In 1999–2000, the extension of Blue Line along an elevated corridor from Tollygunge to New Garia, with six stations, was sanctioned at a cost of ₹907 crore (equivalent to ₹39 billion or US$450 million in 2023).

[11][15][23] The master plan of the metro corridor was made in 1971 along with the North–South Corridor, connecting the office district of Bidhannagar with the twin city and transportation hub Howrah via another transport hub of the city, Sealdah, and the central business district Esplanade by an underwater metro line.

Per the 1971 master plan, the East-West Corridor was supposed to pass under Central metro station, so the square foundational beams in Esplanade were not removed.

[28][29][30] In September 2019, during the construction of the eastbound tunnel (from Esplanade to Sealdah), a TBM hit an aquifer under Bowbazar, causing a major collapse in the area, delaying work in that section for several months.

[40][41] In 2009–2010, Blue Line underwent upgrades of services and amenities and many stations were renamed after famous personalities by then Minister of Railways Mamata Banerjee.

(except between Esplanade - Sealdah) Blue Line has a total length of 32.13 kilometres (19.96 mi) serving 26 Kolkata Metro stations, of which 15 are underground, 9 are elevated and 2 at-grade.

It was the first underground railway to be built in India, with the first trains running in October 1984 and the full stretch that had been initially planned completed and operational by February 1995.

[52] The line from Sector-V to Salt Lake Stadium was inaugurated on 13 February 2020 by the then Minister of Railways Piyush Goyal after 11 years of construction.

On 6 March 2024, the Esplanade - Howrah Maidan section was inaugurated by Prime Minister Narendra Modi, leaving only 2.9 km between the two functional stations to be joined.

[71][72][73] As for a major latest update on 13 January 2025, the remaining 2.9 km between the two functional stations, Esplanade and Sealdah has been successfully connected.

[10] This plan was scrapped and a new metro line from further south in Joka to BBD Bagh was sanctioned in 2010–2011 with a total length of 17.22 km (10.70 mi) at an anticipated cost of ₹2,619.02 crore (equivalent to ₹59 billion or US$680 million in 2023).

[77] Defence Ministry objected that the elevated corridor would overlook the Eastern Command headquarters at Fort William, Ordinance Depot at Mominpore.

[79][80][81] It is India's first metro line to run on indigenous head hardened rails, manufactured by Jindal Steel & Power.

[84] After a series of discussions and consultations with the Ministry of Defence and Government of West Bengal in 2016, it was decided to shift the station around 1 km (0.62 mi) northward, near the Alipore Bodyguard Lines.

[85] But, after a year Defence Ministry approved the Mominpur metro station in its original location as the change in alignment would have delayed the project and budget overrun.

[85] In 2020, the Defence Ministry eased out the process as lease rent wasn't required anymore for tunneling as long the overground ownership of the land did not change.

On 12 January 2025, it was reported that Metro authorities decided to extend the line to Eden Gardens instead of Esplanade to facilitate commuters and connect Strand Road, BBD Bag and Calcutta High Court.

[89] Due to multiple delays and hurdles, the total cost of the project had grown to ₹4,829.57 crore (equivalent to ₹65 billion or US$750 million in 2023).

The key routes were:[101] Since the formation of the Metropolitan Transport Project (MTP) in 1969, Kolkata Metro has always been under the Indian Railways, directly or indirectly.

[114] Kolkata Metro has launched its own official mobile app 'Metro Ride Kolkata' for android & iOS smartphone users which provides information regarding station, train timing, fare and has online smart card recharge facility along with mobile QR code ticketing.

Since the Kolkata Metro has 750 V DC third rail electrification, electricity substations were built in Jatin Das Park, Central and Shyambazar.