It commenced full operations on December 12, 2000; using the Japanese calendar this reads "12/12/12" as the year 2000 equals Heisei 12.

The line is deep (as low as 48 metres (157 ft) below ground at points) through central Tokyo, including three underground crossings of the Sumida River.

[2] However, Singapore's Downtown MRT line stages 1–3 completed in 2017 are 2.84 times as expensive, at 33,669.5 compared to 11,571.8 US dollars per kilometer after adjusting for inflation and international price differences.

In per-kilometer terms New York's Second Avenue Subway Phase 1, also completed in 2017, is over 5.5 times costlier at 2,308.3 compared to 416.3 price-adjusted US dollars per kilometer.

[3] Ridership projections originally estimated 1 million users daily, a figure scaled down to 820,000 before opening.

[4] However, its ridership has increased by about five percent each year since its opening, following new commercial and residential development around major stations such as Roppongi and Shiodome.

Prior to the completion of the Oedo Line loop in 2000, servicing was performed at a depot near Hikarigaoka Station.

Because of differences in infrastructure and technology used preventing trains on either line from accessing the other, a special Toei Class E5000 locomotive powers these ferry runs during overnight hours when the subway is closed.

This plan was amended in 1972 to complete the loop back to Shinjuku, extend it to Hikarigaoka and add a spur line to Mejiro from the northern side.

Following the addition of Shiodome, the automated announcements in the trains were changed to advertise businesses and facilities near each station, a first in Tokyo (although this was already the practice on the municipal subways of Osaka and Nagoya).