The central section of L3 has the city's oldest metro stations, built in the mid-1920s, with additions almost every decade since then.

Its current termini are Zona Universitària, which serves the University of Barcelona campus located on the western end of Avinguda Diagonal in Les Corts district, and Trinitat Nova in Nou Barris.

It was operated by now defunct Compañía del Gran Metro de Barcelona (GMB).

Nowadays it covers a V-shaped area between the west end of Avinguda Diagonal (Zona Universitària) and Canyelles as a result of the integration of the original L3 and a subsidiary line called L3B or L3bis which appeared in 1975 joining Drassanes with Zona Universitària, and which became part of a larger L3 in 1982 when the infrastructures of both joined and they became fare-integrated.

A section of the original L3 disappeared as plans to extend it in that direction would have required too much effort and the construction of L4 provided coverage for the line.