Between 1943 and 1967 he served in various capacities, including SDPO in Chittagong District (pre-independence Bengal), responsible for liaison with the Indian Army during the war.
In 1967, he succeeded another life-long friend, P. K. Sen, as Commissioner of Police, Calcutta, just as the Naxalite movement got into high gear.
He was hated by not only the ultra-left radicals and human rights activists for his ruthless line of action, but also by mainstream politicians.
[1][2] During the troubled Naxalite movement days, as Commissioner of Police, he worked directly under Govind Narain, who was the Union Home Secretary.
He returned in 1972 as IG of West Bengal (then police chief; the post of Director General had not been created, and came in with his successor) and continued till July 1976.
Prasun Mukherjee, a senior police officer who served under him, in an obituary tribute said, "In the departure of Mr Ranjit Gupta, we have lost a person who had become a legend during his career, who was a born leader of a force, was confident of himself, trusted his juniors and identified himself with them so much that he called himself a Policeman and not a Police Officer.