The line first took on its current form between 1985 and 1987 when the section Cornellà-Riera – Sant Josep was first moved underground, followed by the section Sant Josep – Espanya. In 1997 Magòria-La Campana station opened, followed by Molí Nou – Ciutat Cooperativa station in 2000.
An extension of the line further into central Barcelona, with a new station in Plaça Francesc Macià is being projected at the moment. It would link both the metro line and the Baix Llobregat line with Trambaix routes T1, T2 and T3 and the Vallès line. The line is also projected to extend into Besòs Parc station in the Sant Martí district of Barcelona, and a branch line is also projected to link the (future) Cristòfol de Moura station with the Autonomous University of Barcelona campus via the "Horta tunnel".