In 1962, he was made the additional judge of the Allahabad High Court. Later in 1963, he retained his position as the permanent judge of the court. In 1972, he was elevated as the Chief Justice of the Himachal Pradesh High Court. On 20th February 1978, he was appointed as a Supreme Court judge. Subsequently, on 21st December 1986, he became the Chief Justice of India. After his retirement in 1989, he became the judge of International Court of Justice.
He is one of the few judges who can reach the International Court of Justice in The Hague and become one of its judges. In this capacity, he served from 1989 to 1991. In 2005, he also chaired an enquiry into the case of oil for food program, which was one of the cases that came up before the International Court of Justice. In this case, the committee formed by Justice Pathak submitted a detailed report to the Government of India which pointed towards the involvement of Congress leaders like K Natwar Singh and his son Jagat Singh in the mishandling of United Nations oil for food programs contracts.
As a lawyer, he had expertise in areas of law such as constitutional law, income tax, sales tax and other taxation laws; civil law, company law and industrial dispute cases and, he is popular for his role in the case of Bhopal gas tragedy. In this case, he delivered a judgment in favour of Union Carbide company and offered a compensation of 470 million US dollars to the Indian government for the mishap. This judgment has been heavily criticized as it exonerated Union Carbide Company from all criminal liabilities. Therefore, whenJ. Pathak’s name was nominated to the ICJ, there were strong claims that the passage of this judgement was a result of the settlement between him and the company.
He was also on the bench in the case of Kehar Singh v. UOI; he dismissed the mercy petition of the co-accused in the Indira Gandhi murder case.. He is also famous for saying that judges of the Supreme Court with short tenures had a tendency to be more pro-government while adjudicating matters because they were looking for post-retirement employment within the government.Such a trend was something that was endangering the independence of the Judiciary.
Justice Pathak died of a heart attack in the year 2007 at the time he was 82 years old.