Jayakumar served as Singapore's Permanent Representative to the United Nations (UN) and High Commissioner to Canada from 1971 to 1974, and was a member of Singapore's delegation to the UN Law of the Sea Conference from 1974 to 1979.
Jayakumar menjabat sebagai Wakil Tetap Singapura ke Perserikatan Bangsa-Bangsa (PBB) dan Komisaris Tinggi ke Kanada 1971-1974, dan anggota delegasi Singapura dengan UU PBB Konferensi Laut 1974-1979.