The cabinet secretary (ISO:मंत्रिमंडळ सचिव) is the top-most executive official and senior-most civil servant of the Government of India. The cabinet secretary is the ex-officio head of the Civil Services Board, the Cabinet Secretariat, the Indian Administrative Service (IAS), and all Civil Services of India work under the rules of business of the government.

The cabinet secretary is the senior most cadre post of the Indian Administrative Service, ranking eleventh on the Indian order of precedence. The cabinet secretary is under the direct charge of the prime minister. Since 2010, the cabinet secretary's term length was extended to a maximum of four years. Thereafter, amended in 2019 for further extension up to 1 year. In, total up to 5 years.

The precursor to the cabinet, the Executive Council of the viceroy, used to have a secretariat, which was headed by the private secretary of the viceroy. At first, the role of this secretariat was merely to take care of the paperwork related to the Executive Council but when the work of the individual departments under the council increased, the work of the secretariat too became more complex. The private secretary came to be known as the secretary of the secretariat. And this post became more powerful over time as the secretariat's main role became coordinating the work of the departments. In 1946, the secretariat became cabinet secretariat and the secretary became the cabinet secretary.

The following are the functions of the cabinet secretary:

In the Government of India Allocation of Business Rules, 1961, the Cabinet Secretariat finds a place in the First Schedule to the Rules. The subjects allotted to this Secretariat are, firstly, secretarial assistance to Cabinet and Cabinet Committees, and secondly, the Administration of the Rules of Business.

The Cabinet Secretariat is responsible for the administration of the Transaction of Business Rules, 1961 and the Allocation of Business Rules, 1961 of the Government of India, facilitating smooth transaction of business in ministries/departments of the Government by ensuring adherence to these rules. The Secretariat assists in decision-making in Government by ensuring Inter-Ministerial coordination, ironing out differences amongst ministries/departments and evolving consensus through the instrumentality of the standing/ad hoc Committees of Secretaries. Through this mechanism, new policy initiatives are also promoted.

The Cabinet Secretariat ensures that the President of India, the Vice-President and Ministers are kept informed of the major activities of all departments by means of a monthly summary of their activities. Management of major crisis situations in the country and coordinating activities of the various ministries in such a situation is also one of the functions of the Cabinet Secretariat.

The Cabinet Secretariat comprises three wings: Civil, Military and Intelligence. The Civil wing is considered to be the main wing and provides aid, advice and assistance to the Union Cabinet. The purpose of having the Military wing is to have better coordination in Intelligence and to provide secretarial assistance to the Defence Committee of the Cabinet and the National Defence Council. The Military wing is represented by an officer of the rank of major general, or its equivalents in the Indian Armed Forces, who is designated as a joint secretary in the Cabinet Secretariat. The Intelligence wing deals with matters pertaining to the Joint Intelligence Committee of the union cabinet. The chief of the Research and Analysis Wing (R&AW) also officially first reports to the cabinet secretary, and is designated Secretary (R) in the Cabinet Secretariat.