The Principal Secretary to the Prime Minister of India (PS to the PM; ISO: Bhārat Ke Pradhānmantrī Ke Pradhān Saciv) is the administrative head of the Prime Minister's Office.

The Prime Minister's Secretariat (PMS)—headed by an officer of the rank of joint secretary to the Government of India—was established after independence under the prime ministership of Jawaharlal Nehru, as a successor to the office of the Governor-General of India's secretary.

[7] Lal Bahadur Shastri appointed Lakshmi Kant Jha, an Indian Civil Service officer, as his secretary, making Jha the first secretary to the Government of India-ranked officer in the PMS.

[9] During Indira Gandhi's tenure as prime minister, the post of Principal Secretary to the Prime Minister was created;[2][4][8] with retired Indian Foreign Service officer P. N. Haksar becoming the first PS to the PM.

[6][12][13][14] The main functions of the officeholder often include, but are not limited to: The Principal Secretary to the Prime Minister is generally considered the latter's most crucial aide.