After testing in 2014, the first segment of the metro between the Alandur and Koyambedu stations on the Green Line began operations on 29 June 2015.

The underground stretch from AG-DMS to Washermanpet of Blue Line opened on 10 February 2019, completing phase 1 of the Metro.

[12] In December 2007, the Chennai Metro Rail Limited (CMRL) was established as a joint venture between the Governments of India and Tamil Nadu to execute the project.

[18][19] In January 2011, a joint venture between Larsen and Toubro (L&T) and Alstom was awarded the contract for design and construction of track works and a depot at Koyambedu for ₹4.49 billion (US$52 million).

[26] The contract for power supply and overhead electrification was awarded to Siemens for ₹3.05 billion (US$35 million) and contracts for automatic fare collection (AFC), tunnel ventilation and air conditioning were awarded to Nippon Signal, Emirates Trading Agency and Voltas, respectively.

[32] The project faced several delays and missed deadlines due to problems with land acquisition and cancellation of construction contracts.

[36][37] The metro received the statutory speed certification clearance from the Research Design and Standards Organisation (RDSO) in August that year.

[41][42][43] On 17 June 2015, a 30-year-old man was killed and another motorcyclist injured when an iron rod fell on them at a metro construction site near Officers Training Academy at St. Thomas Mount.

[48] On 10 February 2019, the underground stretch from AG-DMS to Washermanpet of blue line was opened, marking the completion of the first phase of the metro.

[53][54] The line opened for passenger traffic on 14 February 2021, increasing the length of the operational metro system to 54.1 km (33.62 mi).

[55] In 2021, the CMRL proposed a further extension of the blue line to connect the airport with Kilambakkam at an estimated cost of ₹46.25 billion (US$530 million).

In July 2016, the Government of Tamil Nadu announced that the second phase would have three lines spanning 104 km (65 mi) with 104 stations.

In July 2017, the state government announced an extension of Phase II, involving a section from Lighthouse up to Poonamallee with an intersection with the Madhavaram–Sholinganallur line at Alwarthirunagar.

[63] In 2019, the Madras High Court questioned the state government on the construction method of the tunnels and its impact on the water bodies.

[80] In December, the CMRL awarded the contract to ST Engineering for the installation of platform screen doors in the elevated stations of the second phase.

[81] In the same month, Shellinfo was awarded a contract ₹42 crore (US$4.9 million) for the installation of automated fare collection systems.

[84] In 2022, the state government proposed an extension plan spanning 93 km (58 mi) for the three under construction lines of the second phase.

[102][103] Feasibility studies for the project was commissioned in February 2023 by the Chennai Unified Metropolitan Transport Authority (CUMTA).

[106] The CMRL is also involved in the feasibility studies for the development of metro rail transport in the cities of Coimbatore, Madurai and Tiruchirapalli.

[115] The trains are air-conditioned with electrically operated automated sliding doors and have a first class compartment with a dedicated section reserved for women.

In the underground sections, a walkway runs along the length with cross passages every 250 m (820 ft) for the maintenance and emergency evacuation.

[125] The stations are air-conditioned and are equipped to be disabled and elderly friendly, with automated fare collection, public announcement system, electronic display boards, escalators and lifts.

[127] Chennai Metro maintains a major depot at Koyambedu covering an area of 26 ha (64 acres) which houses maintenance workshops, stabling lines, test tracks and a washing plant for the trains.

[128][129] In 2022, an elevated depot at Wimco Nagar, covering an area of 3.5 ha (8.6 acres), commenced operations with facilities for inspection, emergency repair, and a washing plant.

[132][133] The main operational control center (OCC) is located in Koyambedu where the movement of trains and real-time CCTV footage obtained is monitored.