Thapar established Karam Chand Thapar & Bros. Ltd. - the parent company of Karam Chand Thapar & Bros. (Coal Sales) Ltd. (KCT). Having gained some experience of the coal industry in his youth, Thapar set out to establish his own coal trading business based out of the Jharia coalfields in 1919. Soon thereafter, he realized that the epicenter of the coal business was not where the mines were located, but in Calcutta, the then established base of all the large European owned mining companies.