Realization of the ideafortram lines in Sofiabegin onDecember 1, 1898when the municipalitygrants concessionsfor construction tocompanies fromFrance and Belgium.Construction workcontinuedfor about a yearandon January 14,1901the firsttram inSofia officially sets off.Initially,passengers wereserved by25 tramsand 10woodenbodied trailersthat ran on6 single tracked routeswitha total length of23 kmand width of1000mm.
From 1903 to 1931, a large number of railcars and trailers were delivered from European manufacturers. In 1931, under the supervision of Mr. Theodosius Kardalev was started the construction of the first Bulgarian trailers that use robust chassis from scrapped railcars. These trailers are known as "Kardalev trailers." In 1936 he produced the first Bulgarian trains called "ДТО" (after the Department of trams and light in the capital municipality). In the production are used old chassis, and all other elements are replaced with new ones.
In 1934 was built the first major depot in today's metropolitan area Krasno Selo. There in 1951 was started a factory for production of trams, the succeeded Kardalev’s Technical Workshop of "ДТО". By 1959 155 locomotives "ДТО" and "Република" were produced- the first all-Bulgarian trams. The last Bulgariantram- T8M-900 was manufactured in the factory in 1991 Since then the factory is mainly engaged in repairing and renovation of old trams.
In 1987 according to European standards was constructed the first tram line with gauge of 1435 mm (current line № 20). Until then, all tram lines in Sofia were narrow (gauge 1009 mm). 8 years later, in 1995, was completed the construction of the second line with gauge of 1435 mm (current line № 22).
On February 17, 2010 is opened line number 23 which connects area “Дружба 2” and area “Дружба 1”. Subsequently the line was extended and so it connects “Дружба 2”and “Младежки театър”.
On April 10, 2010 opened a new tram line with a number of 4 supporting TM5. It’s route is: boulevard “Nikola Petkov” – “Македония” Square - Central Station – area “Орландовци”.
In February2014, after34 yearsonthe streets of Sofia, were decommissionedtheT8M-301 and Bulgaria1300 tram series, which serviced lines 1,4, 5, 6, 7, 11, 15, 17, 19.
FromMay 26, 2014the T6MSofia-400-100 railcar series where also decommissioned. Over 30years they haveserved differentlines -2, 3, 4, 5, 6, 7, 8, 10, 11, 12, 15, 16, 19.