Widely considered a doyen of Constitutional Law, he had argued a number of landmark cases before the Supreme Court.

Thereafter when Mr. NC Chatterjee left for Kolkata, due his ailing health in 1967, he joined the chambers of his former teacher, Shri Raja Vasudev Pillai, Senior Advocate.

He was Advocate-on-Record for the State of Andhra Pradesh and a Junior Standing Counsel for the Central Government before he was designated as Senior Advocate by the Supreme Court in August 1976.

When these proclamations were challenged in the Supreme Court by lawyers such as Soli Sorabjee, Ram Jethmalani, Shanti Bhushan and others who generally represented the opposition parties, Rao defended the Proclamations representing the States of Madhya Pradesh and Himachal Pradesh which were then under President's Rule.

Rao conceived, developed and presented the argument based on secularism which is part of the basic structure of the Constitution and convinced the Court that all the four BJP Governments had acted in concert and violated the basic feature of secularism by mobilising, encouraging and supporting the Kar Sevaks who demolished Babri Masjid.

He successfully fought against capitation fees in educational institutions in J.P. Unnikrishnan's case (1993); for the privileges of members of parliament in P.V.

Narasimha Rao's case (1998); for the Governor's power to appoint a Chief Minister who is not a member of the Legislature, but enjoying majority support while her appeal against conviction was pending in B.R.

He successfully defended the constitutional validity of Entry Tax before a nine Judge Bench of the Supreme Court in 2016.

[citation needed] Rao along with other like-minded lawyers and citizens organised a National Convention for Communal Harmony and Constitutional Objectives in Delhi in April–May 1993, after the demolition of Babri Masjid, securing the participation of many renowned persons from different fields, including retired Judges of the Supreme Court and High Courts, Members of Parliament past and present, former Ministers, administrators including former Cabinet Secretaries, Governors, academicians, journalists and others.