The Constitution of India, 1950 prescribes the "Establishment and Constitution of Supreme Court" under Article 124. According to Article 124(1) the Supreme Court consists of Chief Justice of India and such other judges. Under Article 124(2) the conditions for appointment of the judges of the Supreme Court including the CJI are:
The first proviso to Article 124(2) ("Provided that in the case of appointment of a Judge other than the Chief Justice, the Chief Justice of India shall always be consulted.") clarifies the assumption of inclusion of CJI in the phrase "Every Judge of the Supreme Court" in it. Under Article 124(3), the eligibility criteria to be considered for appointment as a Judge of the Supreme Court including CJI are:
Article 124(6) prescribes post-appointment mandates for the Judge of the Supreme Court including CJI i.e. "Every person appointed to be a Judge of the Supreme Court shall, before he enters upon his office, make and subscribe before the President, or some person appointed in that behalf by him, an oath or affirmation according to the form set out for the purpose in the Third Schedule."
According to the "Memorandum Showing the Procedure for Appointment of the Chief Justice of India and Judges of the Supreme Court of India", published on the official website of Department of Justice, the following are the requisites to be appointed as CJI:
What is meant by senior-most judge?
Seniority is decided on the basis of experience in the Supreme Court and not according to age of the judges. So, the date of induction to the Supreme Court usually settles the seniority. But, in cases where date of induction to the Supreme Court is same then whoever takes the oath earlier becomes senior for this purpose. If the second filter also falls on same day then, the experience. Also the appointments made directly from the bar are taken as subservient to the appointments made from bench for this purpose. So, the outgoing CJI submits its recommendation for the next CJI (which is generally the senior-most judge of the Supreme Court) to the Union Minister of Law, Justice and Company Affairs at least a month in advance after consultation with the other senior judges of the Supreme Court. Then the recommendations are put by the Union Minister of Law, Justice and Company Affairs before the Prime Minister who advises the President in this regard. The President appoints the Chief Justice of India till the age of retirement under his seal.
Whether "seniority rule" is mandatory to be observed?
According to Second Judges Case (Supreme Court Advocates-on-Record Association v. Union of India, AIR 1994 SC 268) "the senior-most Judge of the Supreme Court considered fit to hold the office." And consultation under Article 124(2) is required only "if there be any doubt about the fitness of the senior-most Judge to hold the office, which alone may permit and justify a departure from the long-standing convention."
Why Senior-most Judge of the Supreme Court has to be only appointed as CJI?
The rule of seniority was necessitated to be observed by all the then serving judges in the Supreme Court in 1951 after the passing away of the then Chief Justice of India H.R.Kania. They unanimously put the threat of resignation in case the Government does not observe it. The rule of seniority is an assurance of independence of judiciary by reducing the scope of the discretionary powers of the government.
Was there any deviation from the conventional rule of seniority for the appointment of the CJI?
On April 25, 1973, a day after the judgment of Kesavananda Bharati v. State of Kerala ((1973) 4 SCC 225) which made the legislative and executive actions of the government susceptible to the test of 'basic structure' vide majority of seven among thirteen judges, J. Ajit Nath Ray, one among the six dissenters in this case was appointed as Chief Justice of India superseding the three senior judges J.M. Shelat, K.S. Hegde and A.N. Grover (they belonged to the majority in this case). To which, Former Attorney General for India C.K. Daphtary remarked "the boy who wrote the best essay won the first prize". And Former Chief Justice Mohammad Hidayatullah termed it as a drive of "not forward looking judges but judges looking forward to their future".
On January 29, 1977, the majority player in Kesavananda Bharati case and the lone dissenter in Additional District Magistrate, Jabalpur v. Shivakant Shukla (AIR 1976 SC 1207)' J. Hans Raj Khanna, the then senior-most judge of the Supreme Court of India, was superseded by J. Mirza Hameedullah Beg. The case had affirmed the right to judicial remedy for habeas corpus even during emergency. The Former Chief Justice M.N. Venkatachaliah said the decision deserved to be "confined to the dustbin of history".