The earliest of the Kerala State Road Transport Corporation was the Travancore State Transport Department, constituted by the King Chithira Thirunal Balarama Varma, with the intent of reorganizing the transportation services of the former state. E.G. Salter, Assistant Operating Superintendent of London Passenger Transport Board, was appointed as Superintendent of the Transport Department on 20 September 1937. The Transport Department grew with nationalisation of key interstate routes such as Thiruvananthapuram–Kanyakumari route and the Palakkad–Coimbatore route.
The first fleet consisted of 60 Comet chassis fitted with Perkins diesel engines, imported from England. The bodies of the buses were built by the staff of the Travancore State Transport Department under the supervision of the Superintendent. The model for the selection of operating staff continues to be followed by the current operating staff. The Transport Department gave preference in recruitment for those who were likely to lose their private transport company jobs resulting from the nationalization of Thiruvananthapuram–Kanyakumari route. Thus the Transport Department began with a staff of about a hundred graduates appointed as Inspectors and Conductors.
The State Motor Service was inaugurated by The King Chithira Thirunal Balarama Varma on 20 February 1938. He and his kin were the first passengers of the system on the inaugural trip; Superintendent Salter was the driver of the bus. This bus, along with the thirty-three other buses brought on road driving through the Kowdiar Square was an attraction at that time.
Following the enactment of the Road Transport Corporation Act in 1950, the Government of Kerala formulated KSRTC rules in 1965 by Section 44. The Transport Department was converted into an autonomous corporation on 1 April 1965 and the Keralacation dated 15 March 1965. KSRTC buses are the registered under a dedicated RTO at Thiruvananthapuram with the registration series KL-15.