Yurakucho Line through-running network

The network's connections were planned long before they opened. On 5 September 1968 the Teito Rapid Transit Authority — the predecessor of today's Tokyo Metro — and Seibu Railway exchanged a memorandum agreeing to run mutual through-services, aiming to link the planned Line 8 (the Yūrakuchō Line) with the Seibu Ikebukuro Line by around 1973. The line opened in stages from 30 October 1974, when the first section between Ikebukuro and Ginza-itchōme entered service. Through-running itself began on the Seibu side: on 1 October 1983 the Seibu Yūrakuchō Line opened between Kotake-mukaihara and Shin-Sakuradai, and trains started running through between the two railways — the first through-service of the network.

The Tōbu connection followed with the line's northwestern extension. On 25 August 1987 the segment from Eidan-narimasu (now Chikatetsu-narimasu) to Wakōshi opened, and through-running with the Tōbu Tōjō Line began at Wakōshi, with trains continuing to Kawagoeshi and, for depot-working services, Shinrin-kōen. The Yūrakuchō Line was completed on 8 June 1988 when the final section from Shintomichō to Shin-kiba opened. The Seibu link deepened in two further steps: on 7 December 1994 the Seibu Yūrakuchō Line was extended to Nerima and Seibu's own trains began running through, and on 26 March 1998 the Seibu Yūrakuchō Line was fully double-tracked, allowing full mutual through-running onto the Seibu Ikebukuro Line as far as Hannō — finally realising the connection first agreed in 1968, twenty-five years after the original target.

A distinctive feature of the network is the corridor it shares with the Fukutoshin Line. Under Tokyo's transport plans the Wakōshi–Kotake-mukaihara section is officially Line 13 — the Fukutoshin Line — while the section south of Kotake-mukaihara is Line 8, the Yūrakuchō Line proper; the northern stretch was nonetheless signed as the 'Yūrakuchō Line' to keep service continuous and avoid confusing passengers. A precursor service known as the 'Yūrakuchō New Line', which opened between Kotake-mukaihara and Ikebukuro on 7 December 1994, was absorbed into the Fukutoshin Line when that line opened on 14 June 2008; from then on Yūrakuchō Line and Fukutoshin Line trains have shared the tracks and station facilities between Wakōshi and Kotake-mukaihara. At Kotake-mukaihara, Tōbu Tōjō and Seibu trains can run onto either the Yūrakuchō Line toward Shin-kiba or the Fukutoshin Line toward Shibuya.

The line's ownership passed from the Teito Rapid Transit Authority to Tokyo Metro on 1 April 2004 with the Authority's privatisation. Later additions to the network include the reserved-seat S-Train, which began running on 25 March 2017; on the Yūrakuchō Line it runs on weekdays only, between Toyosu and the Seibu Ikebukuro Line.

Through-running operates at the northern end on two sides. From Wakōshi, trains through-run onto the Tōbu Tōjō Line to Kawagoeshi (and to Shinrin-kōen in the morning and evening). From Kotake-mukaihara, trains through-run via the Seibu Yūrakuchō Line onto the Seibu Ikebukuro Line to Kotesashi (with some morning and evening services reaching Hannō); some Seibu through-trains run as semi-express, rapid or rapid-express within the Seibu lines, changing service type at Kotake-mukaihara. The reserved-seat S-Train runs on weekdays between Toyosu and the Seibu Ikebukuro Line. The Wakōshi–Kotake-mukaihara section is shared with the Fukutoshin Line, so Shin-kiba-bound Yūrakuchō trains and Shibuya-bound Fukutoshin trains both use this corridor.

• 1968On 5 September 1968 the Teito Rapid Transit Authority (the predecessor of today's Tokyo Metro) and Seibu Railway exchanged a memorandum on mutual through-running, fixing the intent to connect the planned Line 8 (Yūrakuchō Line) with the Seibu Ikebukuro Line; full Seibu Ikebukuro Line through-services were initially targeted for around 1973 but did not arrive until much later.
• 1974On 30 October 1974 the Yūrakuchō Line opened its first section between Ikebukuro and Ginza-itchōme, operating at first with five-car trains; the line was named through a public competition that drew 30,591 entries.
• 1983On 1 October 1983 the Seibu Yūrakuchō Line opened between Kotake-mukaihara and Shin-Sakuradai and through-running between the Yūrakuchō Line and Seibu began, the first through-service of the network.
• 1987On 25 August 1987 the northwestern extension from Eidan-narimasu (now Chikatetsu-narimasu) to Wakōshi opened and through-running with the Tōbu Tōjō Line began; Tōbu depot-working trains ran as far as Shinrin-kōen while the other through-trains terminated at Kawagoeshi.
• 1988On 8 June 1988 the final section between Shintomichō and Shin-kiba opened, completing the Yūrakuchō Line between Wakōshi and Shin-kiba.
• 1994On 7 December 1994 the 'Yūrakuchō New Line' opened between Kotake-mukaihara and a new Ikebukuro terminal, and on the same day the Seibu Yūrakuchō Line was extended to Nerima, allowing Seibu rolling stock to begin running through onto the network.
• 1998On 26 March 1998 the Seibu Yūrakuchō Line was fully double-tracked and full mutual through-running with the Seibu Ikebukuro Line began, extending through-services as far as Hannō — the connection first envisaged in 1968.
• 2008On 14 June 2008 the Tokyo Metro Fukutoshin Line opened; the Wakōshi–Kotake-mukaihara stretch became a corridor shared with the Fukutoshin Line and the former Yūrakuchō New Line section was absorbed into the Fukutoshin Line.
• 2017Seibu's reserved-seat S-Train limited-stop service began running on 25 March 2017. It enters the Yūrakuchō Line on weekdays only, running between Toyosu and the Seibu Ikebukuro Line and stopping within the Yūrakuchō Line only at Iidabashi and Yūrakuchō.
• 2022On 6 August 2022 one-person operation was extended to the Kotake-mukaihara–Shin-kiba section, completing one-person operation across the whole Yūrakuchō Line.