Main article: Onew was discovered at the 2006 SM Academy Casting. He received great appreciation from, SM Entertainment's founder, at Girls' Generation's debut showcase.
Lee Soo-man noticed him and wanted to hear him sing during a one time on the spot audition. He signed the contract with the company the day after he auditioned. In 2008, he was chosen as the leader of the group, and the five member boy group debuted on May 25, 2008 on '. Shortly after debut, Onew contributed to singles for in 2008, for Vanilla LOVE and Vanilla Love Part 2.
In 2009, he was featured with member for the song One Year Later in the mini-album. The same year, he also sang a duet with for the song, The Name I Loved from the third mini album by Shinee,. 2010–2017: Musical acting, acting debut and solo activities [ ] In 2010, Onew tried his hands at songwriting and together with his bandmate Minho, wrote the lyrics for the song, 'Your Name' from Shinee's second studio album. In addition to music, Onew became an MC of two programs – 's Night Star, which he co-hosted alongside,, movie director Jang Hang Joon, and 's and 's. Since his first job as an, Onew has gained experience through the years and was active as a presenter for different television networks and events like Dream Concert, ' Incheon K-Pop Concert and also 's special event in Taiwan called Nihao Taiwan.
Onew starred in various musicals starting from 2010, debuting in the musical Brothers were Brave alongside singer Lee Ji-hoon. He then starred in the Korean production of playing the lead role, Drew.
Onew has also showcased his acting skills via television like having a cameo role as a clumsy doctor in the drama. He appeared in the drama's final episode. He also had cameo roles in the dramas, Oh My God x2, Pure Love and for sitcom Royal Villa.
Also, Onew recorded a song titled for the drama series. The song was released in the album To The Beautiful You OST Part 2 on August 22, 2012. Onew also sang the soundtrack Moonlight for drama.