Acting career
In 2010, he was cast in Jungle Fish 2, a youth drama which tackles real life issues about students. He participated in the OST for Jungle Fish 2, singing the song "슬픈예감 (Feeling Sad)" with Hong Jong-hyun.
In 2011, Lee lent his voice for the Korean dub of the film Gnomeo & Juliet.
In 2012 he was cast in Iris II, the sequel to the espionage series Iris.
The same year, he joined the variety show, We Got Married where he was paired up with Oh Yeon-seo in an on-screen marriage.
In 2013, Lee starred in the film Rough Play, produced by Kim Kiduk. The film was unusually risque for a pop idol due to the numerous nude sex scenes he had to perform in it.
He won the Best Male Newcomer award at the 1st Wildflower Film Awards for his performance, and was also nominated for the Best New Actor award at the 50th Baeksang Arts Awards and the 23rd Buil Film Awards.
In 2014, Lee had roles in the crime thriller Gap-dong and romance comedy fantasy drama Mr. Back.
In 2015, Lee starred in SBS' black comedy drama Heard It Through the Grapevine, winning accolades at the 8th Korea Drama Awards and 4th APAN Star Awards for his performance. In the same year, he was signed to Prain TPC.
The same year, he featured in the period mystery film The Piper; and lent his voice to the animated zombie film, Seoul Station.
In 2016, Lee starred in OCN's fantasy thriller The Vampire Detective as the title role. The same year, he had a supporting role in MBC's legal drama Woman with a Suitcase. He also co-starred in the action comedy film, Luck Key.
In 2017, Lee Joon starred in KBS2's weekend family drama, My Father Is Strange.
In 2021, Lee starred in Netflix Original series The Silent Sea. In the same year, Lee starred in tvN/Netflix fantasy series Bulgasal: Immortal Souls.
In 2022, Lee starred in KBS2' s historical drama Bloody Heart. In Bloody Heart, Lee played the role of Lee Tae who becomes King of Joseon. In same year, Lee Joon held the '2022 Lee Joon Busan Fan Camp' at Busan Metropolitan City's Arpina, Haeundae-gu, Busan.
In 2023, Lee stars in SBS’s picaresque revenge drama The Escape of the Seven. In The Escape of the Seven Lee plays the role of Min Do Hyuk who used to be a gangster whose life is filled with a series of betrayals. It was announced that Lee reprises his role in the second season.