[1] Following this, Lee worked at Korea's Electronics and Telecommunications Research Institute (ETRI) for eight years.

Lee was the Chairman of the ITU-T Focus Group Next-Generation Networks (FG-NGN), as well as the Vice-Chairman of the ITU-T Focus Group IPTV.

[1] Lee served as Vice-Chairman of ITU-T Study Group 13 "Future Networks and Cloud" (SG13) from 2001 until 2008, after which he became Chairman of that group in 2009.

Lee was elected at the 2014 Plenipotentiary Conference in Busan (Republic of Korea), with the term beginning on January 1, 2015.

[2][3] At the 2018 ITU Plenipotentiary Conference in Dubai, Lee was elected to a second term.