Ji left Harvard in the middle of his studies and returned to the newly formed People's Republic of China. He studied chemistry at Tsinghua University in Beijing, with the goal of being a scientist and developing nuclear weapons for the PRC. He was instead selected to be an interpreter and notetaker at the negotiations in Panmunjom that would eventually bring an end to the Korean War, due to his English-language skills. After two years in Korea, he returned to Beijing where he was recruited to become Zhou's English interpreter, accompanying the Premier to the 1954 Geneva Conference, and on Zhou's many other international trips. For most of the next two decades, he was a close aide to Zhou, and a frequent interpreter for Mao, often appearing on Mao's right on the reviewing stand at Tiananmen Square during public celebrations when English-speaking dignitaries were present. He holds the distinction of having been interpreter for Mao Zedong's last two official visits with English-speaking dignitaries, in 1976, months before the chairman's death.