P S Krishnan as secretary to the Government of India conceived and implemented path-breaking initiatives. He was the crucial force behind constitutional and legislative enactments like the Constitution (65th) Amendment Act, 1990, vesting constitutional status in the National Commission for SCs and STs; the SC and ST (Prevention of Atrocities) Act, 1989; and, the Employment of Manual Scavengers and Construction of Dry Latrines (Prohibition) Act, 1993.
P S Krishnan also formulated many schemes for the betterment of the marginalised like the Special Component Plan for Scheduled Castes (SCP) in 1978. His tireless efforts pulled out the Mandal Commission Report from cold storage and he persuaded V P Singh to implement it. Each of these initiatives he helmed was, inevitably, challenged in the courts. With his remarkable acumen, he drafted elaborate arguments to face the judicial process, that ultimately placed them on unassailable legal foundations. Among these were the Mandal legislation and reservations in educational institutions for SCs, STs and OBCs.