The supplementary network approved in 1909 provided for a short line linking the Place de la République to the Porte des Lilas.

It would connect Châtelet station (on Avenue Victoria) to the Porte des Lilas via the Place de la République.

The line was originally intended to follow Rue de Belleville for its entire length, but a change in the route ultimately allowed it to serve Place des Fêtes station in order to provide a connection with Line 7 (on its then route), at the cost of passing under buildings for around 800 m (2,600 ft).

[2] Work began in September 1931,[6] with the exception of the structure under the Place de la République, which had been built at the same time as lines 8 and 9.

The construction of the Jourdain and Télégraphe stations also proved difficult, given their great depth, 20 m (66 ft), and the fairly unstable nature of the ground, made up of inconsistent green clay.

After the Liberation, the operation of the metro gradually resumed with difficulty because of the shortage of coal and therefore of electric traction current, but line 11 was the only one that remained closed as a result of serious deterioration of its infrastructure, including the removal of part of the tracks by the Germans.

In 1950, the first tyres with metal reinforcement appeared on the market, capable of supporting a load of 4 t (4.4 tons) with wheels with a diameter of less than 1 m (3 ft 3 in).

The work was mainly carried out at night so as not to disrupt the operation of the line; however, the service was reduced by one hour in the evening.

The surplus equipment allowed twenty-nine motor cars and thirty-seven trailers to be removed from service, most of which dated back to 1908 and 1909.

[15] In 1967, the line was equipped with a centralised control centre and automated train operation, which was used for the first time on the Parisian network.

[18] As part of the extension of the line from Mairie des Lilas to Rosny-Bois-Perrier, most of the stations underwent renovation and adaptation work, including the creation of new access points.

The rear yard at Châtelet, which was too short to accommodate the future five-car MP 14 metro trains, had to be extended in a restricted space under buildings.

[24] All the new stations would be accessible to people with reduced mobility and new rolling stock, the MP 14, would be put into service on this occasion,[25] in a five-car layout (instead of four since the beginning).

According to RATP studies financed by the 2000-2006 State-Region project contract (Contrat de plan État-région, CPER), this extension would increase the number of passengers on line 11 by 68,700 each working day.

[26] The public consultation launched in 2010 estimated the cost of the project at €820m, to which should be added €140m for the renewal of rolling stock and around €100m for the renovation of existing stations.

[27] The agreement approved by the STIF on 7 October 2015 set the financing requirement at €1,084m (Île-de-France region €500.3m; SGP €305.3m; State, €214.4m; Seine-Saint-Denis €64m) for the extension, to which must be added €214m (RATP €73m; Paris City €61m; Region €56m; State €24m) for the adaptation of existing stations and €151m by Île-de-France Mobilités for the renewal of rolling stock.

Two trends clearly emerged: route 2 was preferred, because it would allow the opening up of the Londeau district in Noisy-le-Sec and would serve two high schools as well as the Domus and Rosny 2 shopping centres in Rosny-sous-Bois.

Furthermore, elected officials and residents were resolutely opposed to the phasing of the project: as a result, the STIF planned to carry out the work in a single stage.

[44] The excavation of the first lot—3 km (1.9 mi) of tunnel, a 200 m (660 ft)-long covered trench and earthworks as well as the installation of diaphragm walls and shafts for the subsequent construction of four metro stations—was awarded to a group led by Implenia in association with partners in a consortium comprising: NGE, Demathieu Bard and Pizzarotti.

In August 2018, the A86 was closed to traffic for a week between Rosny-sous-Bois and Nogent-sur-Marne to allow the sliding of a 1,773 t (1,954 tons)-engineering structure to be installed under the roadway between the future Coteaux Beauclair and Rosny-Bois-Perrier stations.

[45] On 20 September 2019, in the presence of the regional prefect Michel Cadot, the president of the Region Valérie Pécresse and the mayor of Paris Anne Hidalgo, the RATP names the tunnel boring machine Sofia (after the station agent of line 11, Sofia Amalou), which began to dig the tunnel between Les Lilas and Rosny-sous-Bois on 16 December.

[47] In February 2023, Île-de-France Mobilités announced that the line would be closed every Sunday between July and August 2023 to allow the extension work to be accelerated.

The plan, according to Île-de-France Mobilités, was to replace the fleet of Line 11 with the MP 14 series, around the time when the extension to Rosny-sous-Bois opened.

The revisions call for a second extension of Line 11 towards Noisy-Champs, considered a part of the Grand Paris Express project, by 2030, although it is unclear if this goal will be attainable.