Lee was chosen for the position of prime minister by President Moon Jae-in to keep his campaign promise to appoint his de facto deputy from Honam region.

He is the 22nd generation descendant of Grand Prince Wanpung, the 1st son of Yi Jachun as well the older brother of Taejo who is known to be the first King of Joseon.

[18][19] Lee is seen as having close ties with key Japanese politicians, having served many years as a senior member in the Korea-Japan Parliamentarians' Union.

[22] He is also known for his love of Makgeolli, a Korean traditional rice wine, which he used to facilitate communication with his provincial government employees[23] who nicknamed him "Manager Lee" for his attention to detail.

[24] On his first day in office, President Moon nominated Lee as his first prime minister of South Korea right after his inaugural ceremony.

Until Lee's nomination was confirmed by the parliament, Hwang Kyo-ahn, the last prime minister under impeached-and-removed president Park Geun-hye, kept his place.

[28] On 29 November, Lee raised concerns that cryptocurrencies were corrupting the youth of South Korea, remarking “There are cases in which young Koreans including students are jumping in to make quick money and virtual currencies are used in illegal activities like drug dealing or multi-level marketing for frauds”.

[citation needed] In 2020 election, Lee stood for Jongno constituency and defeated the UFP President Hwang Kyo-ahn.

[50][51] In October 2020, Lee brought up the idea of "committee to reform the party (Korean: 혁신위)" which resembles one led by Kim Sang-gon in 2015 under then-party leader Moon Jae-in.

If installed, it is likely to be tasked with introducing measures to reform the nomination process, strengthen its ethics code and prepare the longevity of the party.

[53] In September 2020, as part of Lee's party leader campaign promise to transform the party vigilant to societal issues and prepare the country's future, Lee launched seven task forces dedicated to specific issues from power institution and political reforms to youth affairs and industrial safety and appointed Supreme Council members apart from himself and floor leader as their chairpersons by their expertise.

[54] He also launched one for social tragedy countermeasures led by an assembly member from Ansan, Jeon Hae-cheol, who previously chaired party's Sewol disaster committee.

[55] In October the party founded "Korean Peninsula Task force (한반도TF)" to support ongoing momentum in Korean peninsula towards peace irrespective of leadership changes in Japan and United States and appointed senior assembly members with expertise in foreign and inter-Korean relations as its members and Song Young-gil, the chair of the Assembly's Foreign and Unification Committee, its chair.

[63][64] On 9 March 2021, exactly a year before the 2022 South Korean presidential election, Lee resigned as the leader of his party, triggering a leadership by-election and effectively announcing his candidacy for president.

[59] After new leadership members were elected in May 2021, he met with representatives of SMEs and large corporations urging them to take part in solving youth unemployment and breaking his silence.