P. S. Krishnan is best described as an outstanding champion of the deprived social categories of Indian society. In his three decades long period as an IAS officer, he has been vigorously and consistently working for the advancement and empowerment of the Scheduled Castes (SC), Scheduled Tribes (ST) and Backward Classes (BC). He was also a member of the National Monitoring Committee for Education of SCs, STs and Persons with Disabilities, and a member of the Central Monitoring Committee of the National Mission for Empowering Women.
One of the most significant initiatives by him at the national level was the formulation and initializing of the special component plan for scheduled castes in 1978. He has written a number of papers and articles on various aspects pertaining to SC, ST and BC and authored many books.