[citation needed] While attending Holy Spirit High School, a friend signed him up for an audition with Brothers Entertainment without Joo's knowledge.

After several months of training, he was sent to SM Entertainment in South Korea, and on December 9, 1999, made his debut as one of the two members of Fly to the Sky, along with Hwanhee, at the age of 17.

[citation needed] Joo is a member of Fly to the Sky with Hwanhee, Brian sang and also rapped.

[18] The album's lead single, a ballad titled "Don't Go", topped various South Korean real-time music charts upon its release[15] and was awarded first place on Inkigayo on January 21.

[19] While promoting the album, Joo was diagnosed with vocal cord nodules and had to adjust his schedule to avoid further injury.

[25] On April 7, 2011, Joo released his first mini album, Unveiled, including for its lead single an emotional ballad titled "Love Is Over Now".

[27] To promote the album, Joo went on a solo tour of the United States in June 2011 with stops in Seattle, Atlanta, Los Angeles, and New York.

[28] Upon returning to South Korea, Joo made his musical theater debut in August in a Seoul production of Rent, in which he played the role of Mark.

[29] In 2012 at the Shrine Auditorium in Los Angeles, California, Joo performed as a principal cast member representing the Korean culture in a Broadway-style musical called Loving the Silent Tears and based on Supreme Master Ching Hai's poetry collection to commemorate the 19th Anniversary of Supreme Master Ching Hai Day.