Chiyoda Line through-running network

The network's most distinctive feature is its reserved-seat limited express. On 15 March 2008 Odakyu Romancecar services began running through onto the line, the first reserved-seat limited express to operate on any subway in Japan. Using 60000 series MSE trains, these services connect the Chiyoda Line with the Odakyu network and beyond: Metro Hakone runs to Hakone-Yumoto on the Hakone Tozan Line for visitors to Hakone, Metro Enoshima reaches Katase-Enoshima on the Odakyu Enoshima Line on weekends and holidays, and the commuter-oriented Metro Morning Way and Metro Homeway link Kita-Senju with Hon-Atsugi. Within the subway these limited expresses stop only at Kita-Senju, Otemachi, Kasumigaseki and Omotesando, and they may not be used for journeys made entirely inside the Chiyoda Line; trains stop at Yoyogi-Uehara to change crews but do not pick up or set down passengers there.

A further milestone came on 26 March 2016, when equipment changes allowed JR East, Tokyo Metro and Odakyū commuter rolling stock to operate across all three lines for the first time, having previously required Tokyo Metro trains for the cross-operator runs because of incompatible train radios. The through-running map has continued to shift since: scheduled Tama Line services were cut back from 17 March 2018, withdrawn entirely on 12 March 2022, and restored on 15 March 2025. The Kita-Ayase branch, opened on 20 December 1979 as a passenger extension of the access line to Ayase Depot, was brought into the through network on 16 March 2019, when its platform was lengthened for ten-car trains and direct Kita-Ayase–Yoyogi-Uehara services began. The result is a corridor that, on a single trunk subway, joins a JR commuter line in the northeast with an Odakyu network in the southwest that fans out to mountain, beach and suburban destinations.

Through trains run at both ends throughout most of the day. At the northeastern end they continue beyond Ayase onto the JR East Joban Local Line to Abiko (Toride at peak); the Ayase–Kita-Senju section is a fare-overlap with the Joban Line and the two are operated almost as one. At the southwestern end they run beyond Yoyogi-Uehara onto the Odakyu Odawara Line to Isehara and onto the Odakyu Tama Line to Karakida. Reserved-seat Romancecar limited expresses (Metro Hakone to Hakone-Yumoto, Metro Enoshima to Katase-Enoshima on weekends and holidays, and Metro Morning Way / Metro Homeway to and from Hon-Atsugi) stop only at Kita-Senju, Otemachi, Kasumigaseki and Omotesando within the subway and cannot be used for travel wholly inside the Chiyoda Line.

• 1971On 20 April 1971 the Ayase–Kita-Senju section opened and through-running began at the northeastern end with the Japanese National Railways (now JR East) Joban Local Line as far as Abiko, making this the network's first cross-operator through service.
• 1978On 31 March 1978 the final Yoyogi-koen–Yoyogi-Uehara section opened, completing the line, and through-running began at the southwestern end with the Odakyu Odawara Line to Hon-Atsugi (initially on weekday peak services only, running as a semi-express within the Odakyu network).
• 1982On 15 November 1982 the Joban Local through-services were extended to Toride during morning and evening peak hours.
• 1991On 16 March 1991 through-running with the Odakyu network was expanded to Saturdays and holidays, having previously run on weekdays only.
• 2002On 23 March 2002 scheduled through-services onto the Odakyu Tama Line to Karakida began, operating as a Tama Express via Shin-Yurigaoka — the first time subway-operator trains ran on the Tama Line as regular service.
• 2008On 15 March 2008 reserved-seat Odakyu Romancecar limited-express services began running through onto the line, the first reserved-seat limited express to operate on any subway in Japan, linking the Chiyoda Line with Hakone-Yumoto on the Hakone Tozan Line and Hon-Atsugi on the Odakyu Odawara Line using 60000 series MSE trainsets.
• 2016On 26 March 2016 a full three-operator interworking arrangement began, allowing JR East, Tokyo Metro and Odakyū commuter rolling stock to operate across all three lines for the first time, after equipment was modified to make the through services interoperable.
• 2019On 16 March 2019, after the Kita-Ayase branch platform was lengthened for ten-car trains, direct services began between Kita-Ayase and Yoyogi-Uehara, extending the through-running network onto the short branch built originally as an access line to Ayase Depot.