Lee was an independentGuro District Council member candidate for Sindorim-dongin 1995 but was not elected. He helped Kwon Young-ghil, the presidential candidate of the National Victory for Development 21in 1997. After the party was refounded as the Democratic Labour Party, he subsequently joined and ran for a Seoul Metropolitan Council member in 2002 but lost. Lee ran 8th in the DLP list at the 2008 election but was not elected; in fact, DLP only gained 2 FPTPs and 3 PRs. He was selected as the DLP MP candidate for Eunpyeong 2nd constituency at the 2010 by-election, though he abandoned his campaign. At the 2012 election, both Democratic Unionist Party and Unified Progressive Party agreed to put unity candidates in some constituencies, including Gwanak 2nd. Originally, Lee Jung-hee, one of the co-Presidents of the UPP, won the oppositionpreselection over Kim Hui-chul, the DUP candidate and the incumbent MP. However, Kim subsequently left DUP and ran as an independent candidate, citing that the preselection was rigged. Lee Jung-hee was forced to withdraw, making Lee Sang-kyu to replace her. He received 38.24%, defeating Oh Shin-hwan and Kim Hui-chul. The UPP was banned by the court order on 19 December 2014, in which the elections of its all MPs were nullified. Lee announced his bid as an independent candidate at the 2015 by-election, but then withdrew. In the end, the Saenuri candidate Oh Shin-hwan, who lost to Lee in 2012, was finally elected, making him as the first conservative candidate of the liberal-leaning constituency since its creation in 1988. Prior to the 2016 election, Lee joined the People's United Party, a minor left-wing party formed by several notable ex-UPP members. He was selected as the PUP's MP candidate for Gwanak 2nd, but ended up with 1.91%. After that, he shortly left politics and worked as a plumber, till returned to help the party's presidential candidate Kim Sun-dong at the 2017 presidential election. In 2018, Lee announced his bid for Seoul mayorship. In fact, he showed his intention to run in 2010 but endorsed Han Myeong-sook. He lost to Kim Jin-sook in preselection. On 26 August 2018, Lee was elected as the Permanent President of the Minjung Party, received 96%.
Controversy
On 22 May 2012, Lee was questioned by an audience in MBC 100 Minutes Debate, to explain his position and opinion about the issues regarding North Korea i.e. human rights and nuclear. He replied that the question has a problem, adding that people should look the exact appearance of the country. This was criticised by Chin Jung-kwon, saying "All politicians should ensure their ideologies and orientations to the voters. Otherwise, he or she is not supposed to take any duties."
Personal life
Lee married to Kim Hyang-soo, who is 15 years younger than him. Both have 3 children.
