He became a member of Indian National Congress in 1940. As President of the Youth Congress of Coimbatore District he organised the conference in 1949 which was attended by the Hon'ble Kesker, Union Minister among others. He was elected as an MLA in 1952 from Pollachi which he represented till 1967.

He was instrumental for implementation of a number of rural development programmes in Pollachi Taluk where over Rs.35 lakhs was spent. He was also instrumental for implementation of major irrigational schemes such as Parambikulam Aliyar Project costing around Rs.40 crores to provide irrigation to 2.5 lakhs acres in Pollachi, Udumalpet, Dharapuram and Palladam taluks to protect agriculture from the vagaries of nature.

Dr. N.Mahalingam was a member of the working committee of the coimbatore District Congress from 1953 and was a Treasurer for a long period.

He was a member of the Ad-hoc committee (between 1956 - 59) for municipal Elections. His services were utilised in Madurai District and in Kerala in handling party work.

He has served as a Member of AICC between 1958 and 1968.

When Sri Kamaraj was the Chief Minister and Sri U.N. Dheber, Congress President Sri N.Mahalingam was put in charge of elections in Malabar District in Kerala in 1961. He discharged the duty creditably working in cohesion with Muslim League and PSP against Communist party.

After an analysis of political situation during the mid sixties, Sri.N.Mahalingam proposed for an alliance of Congress with National parties like PSP and CPI to fight the DMK-Swathanthara alliance in Tamilnadu. Though Sri K.Kamaraj showed initial interest, the proposal was not pushed though. Hence PSP and CPI (who were inclined to join the alliance with Congress) joined the DMK-Swathanthara alliance. As a result, though Congress secured 41% of the votes, got only 44 out of 234 seats in 1967 general elections for the Tamilnadu Assembly. Sri N.Mahalingam who contested for Lok Shaba from Coimbatore lost in the election along with top leaders of Tamilnadu.

He moved away from active politics from 1969 to devote added attention to business, industry, education and cultural affairs.