Hyun earned an LLM at Columbia Law School in the United States in 1969.

He worked as a prosecutor until 1978, and was elected to the National Assembly as a member of the Democratic Justice Party in 1985.

Hyun stepped down from the legislature in 1988 and was appointed the government legislation chief under president Roh Tae-woo.

Hyun was credited with implementing Roh's policy of nordpolitik, and as a diplomat, helped South Korea expand bilateral relations with a number of countries, including Hungary, Poland, Yugoslavia, Czechoslovakia, Bulgaria, and Romania.

From 2013 until his death, Hyun taught at the Korea National Diplomatic Academy, a school run by the Ministry of Foreign Affairs.