During the Dandi March in 1931, many members of the Calcutta Corporation were imprisoned. Congress requested Dr. Roy to remain out of prison and discharge the duties of the Corporation. He served as the Alderman of the Corporation from 1930–31 and as the Mayor of Calcutta from 1931 to 1933. Under him, the Corporation made leaps in the expansion of free education, free medical aid, better roads, improved lighting, and water supply. He was responsible for setting up a framework for dispensing grant-in-aid to hospitals and charitable dispensaries.