Lee enlisted on October 25, 2012 for his mandatory military service as a member of the Seoul Metropolitan Police Agency riot police.
He was discharged on July 24, 2014.

For his comeback project, Lee chose Secret Door, a period drama about Crown Prince Sado who was controversially executed through death by starvation by his father King Yeongjo; the series reunited him with Han Suk-kyu.
This was followed by the Jo Sung-hee-directed film Phantom Detective, a modern retelling of the eponymous folk hero Hong Gil-dong as a private detective in the 1990s.

In 2016, Lee starred in tvN's fantasy crime drama Signal together with Cho Jin-woong and Kim Hye-soo, which was critically and commercially successful.

In 2017, Lee starred in the fantasy romance drama Tomorrow, With You opposite Shin Min-a, portraying a CEO of a real estate company who has the ability to travel through time.

He then starred in the biographical period drama film Anarchist from Colony directed by Lee Joon-ik, playing the character of Park Yeol, a self-proclaimed anarchist and revolutionary activist during the Colonial Era of Japan.
The same year Lee starred in the film I Can Speak as a civil servant who also tutors English.

In 2018, Lee was cast in the film Time to Hunt directed by Yoon Sung-hyun.
The same year, he starred in the airport-themed melodrama Where Stars Land alongside Chae Soo-bin.
Lee and co-star Chae Soo-bin were appointed as honorary ambassadors of Incheon International Airport.

In 2019, Lee filmed the travel reality programme Traveller along with Ryu Jun-yeol where the two stars enjoy a backpacking holiday in Cuba.
The same year, he was cast in the film Tomb Robbery.
In 2020, he made a special appearance in the drama "Stove League," showing off his presence.
Lee enlisted on October 25, 2012 for his mandatory military service as a member of the Seoul Metropolitan Police Agency riot police. He was discharged on July 24, 2014.
For his comeback project, Lee chose Secret Door, a period drama about Crown Prince Sado who was controversially executed through death by starvation by his father King Yeongjo; the series reunited him with Han Suk-kyu. This was followed by the Jo Sung-hee-directed film Phantom Detective, a modern retelling of the eponymous folk hero Hong Gil-dong as a private detective in the 1990s.
In 2016, Lee starred in tvN's fantasy crime drama Signal together with Cho Jin-woong and Kim Hye-soo, which was critically and commercially successful. 
In 2017, Lee starred in the fantasy romance drama Tomorrow, With You opposite Shin Min-a, portraying a CEO of a real estate company who has the ability to travel through time.
He then starred in the biographical period drama film Anarchist from Colony directed by Lee Joon-ik, playing the character of Park Yeol, a self-proclaimed anarchist and revolutionary activist during the Colonial Era of Japan. The same year Lee starred in the film I Can Speak as a civil servant who also tutors English.
In 2018, Lee was cast in the film Time to Hunt directed by Yoon Sung-hyun. The same year, he starred in the airport-themed melodrama Where Stars Land alongside Chae Soo-bin. Lee and co-star Chae Soo-bin were appointed as honorary ambassadors of Incheon International Airport.
In 2019, Lee filmed the travel reality programme Traveller along with Ryu Jun-yeol where the two stars enjoy a backpacking holiday in Cuba. The same year, he was cast in the film Tomb Robbery. In 2020, he made a special appearance in the drama "Stove League," showing off his presence.
Lee Je-hoon