He started his career in 1920 as a coal trader in Calcutta, and built up the family fortune through Karam Chand Thapar and Bros.
He also took over the Oriental Bank of Commerce, and ventured into paper manufacturing with the Ballarpur Industries Limited.
As a leader, Thapar managed to consolidate a diverse group of investors and contractors, and incorporate them into his coal distribution network.
Lalit stood by his word to his dying father and did over the years divide the group among his brothers; the fact that he was a life-long bachelor with no children was helpful in this.
However, Lalit gave the reins of the bigger part of the company to Gautam Thapar, son of Brij Mohan, and gave the chemicals division to Vikram Thapar, the son of Inder Mohan.