Following the Indo-Pakistan Partition, the Radcliffe Commission was formed for demarcating boundaries between India and Pakistan. Justice Mahajan’s inclusion in the commission is testimony to the government’s faith in his sagacity and an unbiased judicial approach. As a member of the Commission, he made a momentous contribution by persuading Lord Mountbatten to award District Gurdaspur (initially awarded to Pakistan) to India. Justice Mahajan’s suggestion, that River Ravi should be made the boundary dividing India and Pakistan, was the reason for the change. Only because Gurdaspur became part of India, did it become possible for India to make a road and rail link, connecting Jammu & Kashmir with the rest of the country.

The tumultuous conditions in Kashmir were in full swing when Justice Mahajan took over the reins of administration as Prime Minister of Kashmir on 5th October 1947. Within weeks of assuming his new responsibility, Justice Mahajan successfully convinced the Maharaja of Kashmir Hari Singh that the interest of Kashmir would be best served by acceding to India.While MCM fulfilled the difficult assignment given by Sardar Patel, the then Home Minister of India, indelivering Kashmir to India, he also fulfilled his obligation to the people of Kashmir by ensuring that before the instrument of accession was signed, Indian Army troops had landed at Srinagar by 27th morning and begun their military operations to counter the Pakistani attack. This act of Justice Mahajan speaks volumes of his fairness, fearlessness and great sense of justice. In one stroke he not only protected the interests of Kashmir, of which he was a custodian, but also effectively thwarted the covert efforts of Mohammad Ali Jinnah to annexe Kashmir clandestinely.

As part of the Commission tasked with investigating the reasons behind the Indian Naval Mutiny of 1948, Justice Mahajan and the other members of the Commission managed to uncover the truth behind the mutiny, and boldly held the British Rear Admiral of the Naval Establishment guilty of instigating and perpetuating the same.

Justice Mahajan took over as Chief Justice of India on 4 th January 1954. During his tenure, he took a bench of Supreme Court to Kashmir to decide all cases of state Privy Council transferred to it by the Government of India. During his illustrious tenure, MCM gave some historic judgements, some of which are quoted even today.

From his early years as a jurist, MCM had been actively associated with the activities of DAV College Trust. Post his retirement; he served as the President of the DAV Trust for almost a decade from 1955 to 1964. His integrity and vision has resulted in DAV trust developing into an institution of formidable reputation, known for imparting quality and value based education through its thousands of DAV schools spread throughout the country today.

On the recommendation of an English Chief Justice, Sir Tervor Harris, Justice Mahajan was elected as the Chief Judge of the East Punjab High Court, superseding four sitting judges.

Maharashtra leader Senapati Bapat resorted on hunger strike demanding the government to form a commission which would address border dispute. At Maharashtra's insistence, the Government of India constituted the Mahajan Commission on 25 October 1966. V.P. Naik, Maharashtra's Chief Minister at that time, announced in public on 9 November 1967 that Maharashtra will adhere to Mahajan Commission's report, regardless of the outcome. [6] The commission was headed by the third Chief Justice of the Supreme Court of India, Meher Chand Mahajan. The commission, upon review of Maharashtra's claims, recommended the exchange of several villages in Belgaum district between the two states, but rejected Maharashtra's claim on Belgaum city.
The Mahajan Commission received 2240 memoranda and interviewed 7572 people and submitted its report. Maharashtra had asked for 814 villages besides Belgaum. It was given 262 villages including Nippani, Khanapur and Nandgad. Mysore State had claimed 516 villages, of which Maharashtra admitted that 260 were Kannada-speaking ones. It was awarded 247 villages including claim to Solapur.