 From 1986 to 1990, he was Division Chief at the Foreign Ministry, before serving as counsellor to the North Korean embassy in Zimbabwe from 1990 to 1995.From 1995 to 1999, he was Deputy-Director of the Foreign Ministry.Sin's first appointment to the United Nations came in 1999, when he worked at the North Korean Mission to the United Nations for four years before returning home upon being appointed Director-General of the Foreign Ministry.