[5] In July 2016, Government of Tamil Nadu announced that the second phase would have three lines totaling 104 km (65 mi) in length with 104 stations.

[11] In November 2022, Alstom was awarded the contract to supply metro coaches for the phase II expansion.

[8][16][17] On 14 February 2021, Prime Minister of India announced that the government has set aside ₹63,000 crore (US$7.3 billion) for the construction of phase II and further extension.

[18] In 2022, the state government proposed an extension plan for the fourth line from Poonamalee to Parandur, covering an approximate 43.6 km (27.1 mi).

[19] In early 2024, feasibility report was submitted by CMRL for the proposed expansion of the line, green lighting the same.