The first section of this line was built in the late 1960s between Schuman station and De Brouckère, but was served by trams. The first metro was brought into service on September 20, 1976, and the existing underground section was extended up to Tomberg on line 1B, and up to Beaulieu on line 1A. Line 1B was later expanded to the west, to Saint Catherine in 1977, to Beekkant in 1981, to Saint-Guidon/Sint-Guido in 1982, to Veeweyde/Veeweide in 1985, to Bizet in 1992 and finally to Erasme in 2003. The line was expanded to the east, to Alma in 1982 and to Stockel in 1988.
Currently the line is congested at peak hours, so STIB has plans to divert some traffic via construction of a new leg of the metro. Under provisional plans it would run from Merode to Troon via new stops in Jean Rey Square and the Brussels-Luxembourg railway station.