
In December 2012, Choi joined dance project group SM The Performance alongside labelmates from TVXQ, Super Junior, Shinee, and Exo. In preparation for his role as a high jump gold medalist, Choi received personal training from coach Kim Tae-young, former national high jump athlete and a member of the Korea Association of Athletics Federations, for a month and a half.

The drama started broadcasting on August 15, 2012, on SBS. In 2012, Choi was confirmed to take on the lead role, alongside f(x)'s Sulli and Lee Hyun-woo, in To the Beautiful You, a Korean adaptation of the manga Hana-Kimi. In 2011, Choi was cast in SBS' sitcom, Salamander Guru and The Shadows. He made his acting debut in KBS2's drama special, entitled Pianist, with actress Han Ji-hye. In 2010, Choi joined the variety show Oh! My School as a cast member and began hosting the music program Show! Music Core alongside bandmate Onew, Miss A member Suzy and T-ara member Jiyeon. In 2009, Choi joined the popular show Let's Go! Dream Team as a regular cast member. He was also featured in the music video of VNT's debut song "Sound" in 2010. In 20, Choi appeared in both the Korean and Japanese versions of Girls' Generation's music video " Gee". He was especially pleased with Choi's rap lyrics for Shinee's 2009 single "Juliette".

JQ praised Choi's writing ability and pointed out that he has many good ideas and "a few genius moments here and there". Choi began participating in the rap making of Shinee's songs with their first studio album The Shinee World, under the guidance of rap instructor JQ. The group's first EP, Replay, was released on May 22 and debuted on the Korean music charts MIAK at number ten, peaking at number eight. The five-member boy group debuted on May 25, 2008, on SBS' Inkigayo. One month later, Choi was chosen as a member of the group Shinee. Choi was discovered at the SM Casting System in 2006 and modeled for Ha Sang-beg's Seoul Collection F/W 08–09 in March 2008.
