He was later promoted to Inspector and developed a reputation for raiding illegal gambling dens and cutting down on police corruption.

Thereafter, Kotelwala started his own business ventures, first by managing the stake in the Attygalle family business which he had gained as dowry in his marriage, which included 2,058 acres (833 ha) of rubber and coconut estates, as well as a share of one-fourth of the graphite mines owned by the Attygalle family.

Kotelawala decided to expand into the transportation industry, which was at the time heavily dependent on bullock carts for rural trade.

On his return from Japan, Kotelawala was arrested for orchestrating the murder of Francis Dixon Attygalle, his brother-in-law.

Francis Attygalle was shot dead by Piloris, a man who claimed to be a Boer War veteran and had served under Winston Churchill.