[4][5] Lee achieved commercial success and Hallyu star status after his portrayal as the second male lead in the television series Air City,[6] where he went on to date his co-star Choi Ji-woo for three years.

Lee continued to land lead roles playing the president's son in Formidable Rivals,[7] a plastic surgeon in the series Before and After,[8] and a newly married chaebol in Glass Castle.

[10][11][12] After his military discharge in 2011, Lee starred in his comeback project, Myung-wol the Spy where he played a North Korean agent.

[15] Lee then landed his most high-profile role yet as a TV anchor named Park Sun-woo in the time-traveling romance Nine alongside Jo Yoon-hee.

[19] After that, Lee reunited with the writer and director of Nine in the television series The Three Musketeers, a period drama set during the Joseon era where he played Crown Prince Sohyeon.

[20][21] He continued to star in big screen films, fantasy romantic comedy The Beauty Inside[22] and the time-travel crime romance Time Renegade.

In 2019, Lee signed an exclusive contract with BH Entertainment, which houses many other top high-profile South Korean actors.

[37] In 2020, Lee starred in Netflix original series Sweet Home,[38] a webtoon-based drama about a secluded teen who lives cooped up in his room, scarred from memories of school violence, and experiences creepy events after moving to an apartment following the loss of his family.

[56] On February 14, 2024, it was confirmed that Lee would be returning to the big screen with the film Dark Nuns alongside Song Hye-kyo, Jeon Yeo-been, Huh Joon-ho, and Moon Woo-jin.

Lee is set to star as Father Paolo, a priest and psychiatrist who believes that medicine can cure a young boy possessed by a powerful evil spirit.

[60] On April 29, 2024, ENA confirmed that Lee would be starring in their upcoming romance drama Dear Hyeri alongside Shin Hye-sun.

[63] After starring together in the 2007 South Korean television series, Air City, Lee went on to date his co-star Choi Ji-woo for three years from 2009 to 2011.