The line was opened in August 1936 between Sol and Embajadores, a few days before the beginning of the Spanish Civil War.

In 2007, the platforms were lengthened to 90 metres (300 ft) to allow for 6-car trains of CAF class 3000.

During this process, all of the stations were modernized and rebuilt, thus giving the original section of Line 3 a brand new look.

Moncloa station was completely rebuilt adjacent to that of the Line 6, proving an easy connection between the two lines.

On 21 April 2007, the line was extended from Legazpi to Villaverde Alto, doubling its length.