In 2006, S.M. Entertainment, an entertainment agency based in South Korea, recruited Luna after seeing her performing on a SBS's television program, "Truth Game". After training for more than three years, she became a member of a quintet pop idol girl group, f(x), under the label of her agency. On September 1, 2009, f(x)'s first single "LA chA TA" was digitally released. The group's first broadcast performance of "La Cha Ta" was held at MBC's music show Show! Music Core on September 5, 2009. Since then, f(x), has released three digital singles and a mini-album, Nu ABO, and have won numerous awards. The group participated in the SMTown Live '10 World Tour alongside their label-mates in Seoul, Shanghai and Los Angeles. f(x) has also appeared in their own reality shows like Hello f(x),f(x)'s Koala, Amazing f(x), and Go! f(x). They have also endorsed some commercial products like an LG Cyon cell phone, 'Lollipop', and clothing brands like K-Swiss. On November 24, 2010, Avex Entertainment, released a statement that f(x) was now signed to their agency for future releases in China, Japan and Taiwan.
In 2010, Luna won the 'Variety New Star Award' at the SBS Entertainment Awards for 'Star King'.
In October 2010, Luna was one of the twenty idols from different South Korean groups that recorded the song, "Let's Go", for the purpose of increasing public participation in the 2010 G-20 Seoul summit. She provided vocals along with labelmates Sungmin, Seohyun and Jonghyun.
Also, Luna appeared as the regular member of Star King for a long time and earned an Award from SBS for her appearance and effort.
On April 15, 2011, Luna started hosting a music program called The Show from MTV Korea along with Secret's Hyoseong.
Luna was cast in the TV Chosun drama entitled Saving Ahjumma Go Bong Sil as Seo In Young, a college student and youngest daughter of Go Bong Sil. It was her drama debut alongside SS501's Kim Kyu Jong. It was first aired in December 2011. She also won an award from KBS's Immortal Song 2.
Luna has recorded quite a few tracks for OSTs of various dramas. In late 2009, Luna and Krystal contributed to the soundtrack of television series, Invincible Lee Pyung Kang, with a duet, "Hard but Easy". In early 2010, Krystal, Luna and Amber also recorded the song "Spread Its Wings" for the soundtrack of the KBS's drama, God of Study. Krystal and Luna again recorded a duet song for the KBS's drama Cinderella's Sister original soundtrack, called "Calling Out". In late 2010, Luna released a single title, "Beautiful Day", as part of the soundtrack for KBS's drama, Please Marry Me. On December 23, 2010, a duet collaboration between Luna and Super Junior's Yesung was released, titled “And I Love You“, for the second original soundtrack of KBS's President.