[2][3] In his career as a diplomat, he has primarily represented North Korea in its relations with African countries.
From 1979 to 1983, he was a senior officer in the Foreign Ministry, then, from 1983 to 1986, counsellor at the North Korean embassy to Lesotho.
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.
[2] In his latter role, Sin has been tasked with expressing North Korea's positions on the issue of his country's nuclear activities.
In October 2008, Sin told a session of the General Assembly that North Korea had developed nuclear weapons in response to the threat it perceived from the United States, but that it had begun dismantling its nuclear apparatus and that it supported the "denuclearisation of the Korean peninsular".