[1] In 1712, Governor Harrison (1711–1717) first started a Company Postal Service in Madras to carry mail to Bengal by dak runner.

This warranted establishing a post office in Fort St. George so that the letters of the staff of the company, which were carried free at the expense of the government until then, could be charged for.

[3] Accepting this suggestion, the first Madras Post Office with fixed postal charges—the Madras GPO—was established by Governor Sir Archibald Campbell (1786–1790), who also established the Male and Female Orphan Asylums (that developed as St. George's School), and the postal service was thus made a government facility.

Chennai General Post Office was initially opened in Fort St. George Square, just outside the Sea Gate, on 1 June 1786.

In 1854, a Post Office Act came into force, an organised postal system was established and stamps were first introduced.

In 1856, the Madras Post Office moved to Garden House, Popham's Broadway, near the Kothawal Chavadi market.

The internal carriage of mail in Madras was by horse cart (jutkas) till 1918, though a beginning with motorised transport was made in 1915.

In 1873, the present site, where the Abercrombie Battery had once stood, was selected and the construction started in 1874, but there was a lack of funds to proceed with the work till 1880.

However, the idea was abandoned due to opposition from the Madras Chamber of Commerce, and the post office continued to function from the old building.

[6] The twin towers, when built, sported the Kerala roof-influenced "caps" atop as favoured by Chisholm, influenced by his building assignments in Travancore.

[2] Besides a high-ceilinged central hall, the ground floor provided space for stores, kitchen, servants, and so on.

[4] The Chennai GPO is the primary post office of South India and has the Postal Index Number (PIN) 600 001.

[10] Chennai GPO launched a financial inclusion drive to provide post office Saving account to the poor of the poorest at cost of ₹50 linked with mobile and aadhaar.

[14][15] An aadhaar enrollment centre has also been started in Chennai GPO to help transgender people and other marginalized sections of society.