The "main line" of the metre-gauge railway system in the Coromandel Coast connected Chennai with Tiruchchirappalli via Viluppuram, Cuddalore, Chidambaram, Mayiladuthurai, Kumbakonam, and Thanjavur junctions.

[2][3] In 1861 the Great Southern of India Railway (GSIR) built the 125 km (78 mi)-long 1,676 mm (5 ft 6 in) wide 5 ft 6 in (1,676 mm) broad gauge line between Nagapattinam and Tiruchirapalli (then known as Trichinopoly) and the line was opened to traffic next year.

After taking over of GSIR by South Indian Railway Company in 1874, the Nagapattinam–Tiruchirapalli line was converted to 1,000 mm (3 ft 3+3⁄8 in)-wide metre gauge in 1875.

[5] Again after conversion, the 125 km (78 mi)-long 1,676 mm (5 ft 6 in)-wide broad-gauge line between Nagapattinam and Tiruchirapalli was opened in 2001–02 The South India Railway Company laid a 715 km (444 mi)-long metre-gauge trunk line from Chennai to Thoothukudi via Viluppuram, Cuddalore Port (then known as Cuddalore Junction), Mayiladuthurai, Thanjavur, Tiruchirapalli (then known as Trichinopoly), Madurai, Virudhunagar in 1880.

Following an agreement between the British and the French, a 38 km (24 mi)-long metre-gauge line was laid between Puducherry and Viluppuram around 1877–1879.

[5] A 1,067 mm (3 ft 6 in)-wide line was laid between Arakkonam and Kanchipuram (then known as Conjeevaram) in 1865 by Indian Tramway Company.

[7] The 36 km (22 mi)-long Mayiladuthurai–Tharangambadi (then known as Tranquebar) line which was opened by British for people in 1926 and was closed in 1987 for broad gauge conversion.

The area south of Chennai was served by a single line shared by passenger and goods trains till 1931.

The left over conversion work was then completed and the last metre-gauge EMU service ran between Tambaram and Egmore on 1 July 2004.

[5] In the early 1950s legislation was passed authorizing the central government to take over independent railway systems that were there.