It connects Roi Baudouin/Koning Boudewijn in the north-west of Brussels to Simonis/Elisabeth to the north-west of the city centre, then performing a counterclockwise "loop" around the centre up to Simonis again.

During this loop, the line runs under the Small Ring (Brussels' inner ring road), from Porte de Hal/Hallepoort to Yser/IJzer.

It has existed in its current form since 4 April 2009, when it replaced former line 1A between Roi Baudouin and Beekkant.

The Simonis-Elisabeth loop is also served by line 2.

Starting from Roi Baudouin, the line crosses the municipalities of the City of Brussels, Jette, Koekelberg, Molenbeek-Saint-Jean, Anderlecht and Saint-Gilles.