Though the bus services in the city of Kolkata had its start in 1920, the organized Road Transport in Public Sector was given shape on 31^st July, 1948 with the creation of State Transport Services under the ‘Directorate of Transportation, Government of West Bengal. At the outset, it started the bus operation on 6 (six) city routes with a microscopic fleet strength of 25 petrol driven single decker buses. Diesel era started with the addition of 2 (two) Double Decker buses in 1949-50. In a very short time, from the cradle hood, the State Transport services entered into the stage of self-reliance with the establishment of its own garages/depots to house its buses and the Central Workshop to undertake repair and maintenance jobs.

Gradually the structure of State Transport Services turned into a full- fledged organization with spreading its network of operation throughout the entire city (mainly covering Calcutta Improvement Trust area). After about 12 years, State Transport Services became CSTC (Calcutta State Transport Corporation) on 15^th June, 1960 in terms of Road Transport Corporation Act 1950 with an objective to provide efficient, adequate, economical and properly coordinated passenger bus service particularly in and around the city of Kolkata . The establishment of this STU( State Transport Undertaking) has had some socio – economic reasons in the then political context, which can be mentioned as :–

1. After Independence in 1947, the population of the Calcutta city grew very fast due to influx of population from East Pakistan (now Bangladesh). Thus in order to meet the increased passenger service demand, government of West Bengal decided to take over the transport services of the Calcutta city in its own control, mainly for passenger services.
2. To employ people (mainly immigrants) at large in the public undertaking.

Up to 1966-67 CSTC nationalized about 90% of the City routes. After that CSTC could not sustain the increased passenger demands in the city mainly due to the financial constraints. Since then Government decided to allow private buses to operate in CSTC routes and areas.

C.S.T.C. started its first Long Distance Service on and from 14/04/1968 from Calcutta to Digha mainly to meet increased demand from the tourists. Later to meet the passenger demand of the mofussil areas CSTC started connecting the nearby rural areas with Calcutta by its Long Distance Services. Over the years, with rapid expansions of long distance operations CSTC connected remote rural areas of the state with kolkata. C.S.T.C. operated Long Distance Service from Kolkata to all district Headquarters of West Bengal expect Cooch Behar. In the year 2015 C.S.T.C. discontinued its Long Distance Services operation and as mandated by the Transport Department it became the Primary Public Operator of Kolkata Metropolitan Area.