Lee won 24.3 percent of the entire votes to come out the final winner. The following five including Kim (23.8 percent), Choo Mi-ae (14.1 percent), Kang Ki-jung (10 percent), Lee Jong-kul (8.4 percent) and Woo Sang-ho (7.5 percent) were named new supreme councilors.
"I appreciate all the support as well as the blame placed upon me (during the leadership election campaign),” said Lee, after the announcement.
“I shall devote myself to replacing the current administration (in the December presidential race).”
Lee takes over the DUP after the party was left in leadership vacuum since former chief Han Myeong-sook resigned in April.
Lee’s win is also expected to boost the partisan support of former presidential chief-of-staff Moon Jae-in, who has been dubbed a potential presidential candidate for the DUP.
The former minister held an upper hand over his competitors in the beginning of the race but was faced with obstacles as former floor leader Kim turned the game around by winning in most of the regional primaries.
"The core reason for victory was the support from young voters in their 20-30s,” said Lee’s aide.
The ruling Saenuri Party has been upping the ante against the DUP by questioning its stance on North Korea.
The 60-year-old senior lawmaker served as a close aide to former liberal President Roh Moo-hyun in 2004-2006.
He also worked for the Kim Dae-jung government in 1998-1999 as education minister.