He started his career as a journalist in 2005 at Korean Broadcasting System(KBS), a public broadcaster. He mostly covered national security and inter-Korean peninsula relationship. He exposed that the ruling party of Korea ran an illegal campaign office and paid money to influence internet opinion for presidential candidate Park Geun Hye (now president) in 2012. He and his colleagues also exposed large-scale illegal surveillance of civilians by government agents. In 2012, he received “Journalist of the Year” award of the Journalist Association of Korea (JAK). In 2014, he won the “Gold Remi” in the field of Politics & Commentary in the Houston International Independent Film Festival. In early 2015, he left KBS, Korea's most influential broadcaster, to join KCIJ to pursue independent investigative journalism.