He is also well known for his roles in I Can Hear Your Voice (2013), Doctor Stranger (2014), Pinocchio (2014), W (2016), V.I.P (2017), While You Were Sleeping (2017), Romance Is a Bonus Book (2019), and Big Mouth (2022).

[6] In 2010, Lee made his official acting debut in the South Korean TV series Prosecutor Princess.

Lee started to gain recognition following his supporting role in the hit drama Secret Garden where he played a talented young composer with a surly attitude and a forbidden crush on the second male lead.

[18] Lee then starred in the sports film No Breathing and had a supporting role in the box office hit The Face Reader.

[24] Lee next starred in Pinocchio opposite actress Park Shin-hye,[25] and played the protagonist Choi Dal-po, a first year reporter at a broadcasting company who struggles with the idea of justice and truth in a world where everyone wants to hide the facts.

[32] Due to Lee's success in China, a wax figure of him went on display in Hong Kong's Madame Tussauds, which the actor unveiled himself in a ceremony.

[33] In December 2015, Lee left his previous agency Wellmade Yedang and signed an exclusive contract with YG Entertainment on 10 May 2016.

[34] In July 2016, Lee returned to the Korean small screen with MBC's fantasy thriller W alongside Han Hyo-joo.

The organization also released promotional videos featuring the actor, titled "8 Episodes of Korea", which focused on tourist spots in 10 different regions including Seoul, Gyeonggi, Gangwon, Jeju and Gyeongju.

[52] Later in September 2021, Lee confirmed the MBC drama Big Mouth with Im Yoon-ah, coming back three years after his discharge from the military.

[53][54] In 2022, Lee held a fan meeting 'RE, JONG SUK' at the Blue Square Mastercard Hall in Seoul on 12 September.

Lee was deemed unfit to enlist as an active duty soldier as a result of suffering a car accident when he was 16 and tearing his anterior cruciate ligament.

[67] On 7 March 2022, Lee donated 100 million won to the Hope Bridge Disaster Relief Association to help the victims of the massive wildfire that started in Uljin, Gyeongbuk and spread to Samcheok, Gangwon.