Subbarayan was born to Paramasiva Gounder[1] in the family estate of Kumaramangalam near Tiruchengode, Namakkal district on 11 September 1889.

Hence, the Governor chose Subbarayan, who was not affiliated to either of these parties, to form the Government and nominated 34 new members to the Madras Legislative Council to support him.

[13] Because Subbarayan's regime was appointed and largely controlled by the Governor, it became the target of strong criticism both from the Justicites as well as the Swarajists.

[13] In March 1927, P. Munuswamy Naidu of the Justice Party passed a motion recommending salary cuts for Government ministers.

[15] Fearing the possibility of the formation of a Swarajya Party-Justice Party coalition Government, the Governor stepped in to foster discord amongst the opposition.

[15] Led by the Raja of Panagal, the Justice Party switched sides and lent its support to the Subbarayan government.

[20] This act, it is believed, introduced provisions for reservations for Dalits and increased representation for Indian Christians and Muslims.

[28] The Viceroy, however, refused permission explaining that temple entry was an all-India problem and should not be dealt with in a provincial basis even while clearing Ranga Iyer's bill.

[25] Subbarayan had been a follower of Mahatma Gandhi from his early days[26] and he officially joined the Indian National Congress in 1933.

[26] Subbarayan was an admirer of Indian National Congress leader Chakravarti Rajagopalachari (Rajaji) right from his early days.

[34] Subbarayan actively participated in the Quit India Movement and was arrested along with other Congress leaders as Sathyamurthy and M. Bakthavatsalam.

In 1947, he served as a Minister for Home and Police in the Ramaswamy Reddiar Cabinet in Madras[2][3] and was a member of the Constituent Assembly of India.

[3][37] He was instrumental in the signing of a mutual treaty of friendship with the Indonesian Foreign Minister Mohammad Roem on 3 March 1951.

[42] Subbarayan was a member of the first Official Language Commission constituted by Prime Minister Jawaharlal Nehru on 7 June 1955, under the chairmanship of B. G. Kher.

It recommended a number of steps to eventually replace English with Hindi as the sole official language of India.

Subbarayan and another member – Suniti Kumar Chatterji from West Bengal – did not agree with its findings and added dissenting notes to the report.

[44][45] Later when the Indian President Rajendra Prasad sought his opinion on making Hindi as the sole official language, Subbarayan advised against it.

[34] With Sir John Beaumont and Sikandar Hayat Khan, he formed the commission that investigated the return of Lala Amarnath from the India's tour of England in 1936.

[12] His second son, General P. P. Kumaramangalam was a Second World War veteran and served as India's Chief of Army staff.

Mohan's son and Subbarayan's grandson Rangarajan Kumaramangalam was a minister in Indian National Congress and NDA governments.