He made his Broadway debut at age 10 in 2003 as Young Simba in the Broadway production of The Lion King. In 2004, he appeared as Jackie Thibodeaux in the original Broadway cast of Tony Kushner's Caroline, or Change. He also toured with the company during its five-month run in Los Angeles and San Francisco. Thomas has also performed in the Broadway productions The Lion King, and The Color Purple.
Metro Hearts is a mixtape by Leon Thomas. It was released on August 1, 2012. Songs on the mixtape Metro Hearts include "Forever", "Bad", "Moving On", "Vibe", "Like Clay", and "Never Look Back". The mixtape also included a cover of "Take Care" by Drake, featuring Rihanna. The cover is by Leon Thomas featuring Ariana Grande.
Leon Thomas co-wrote the song "Ain't No Other Me" for the British group Stooshe, which features as a deluxe edition track on their debut album, London with the Lights On. Thomas co-wrote 4 songs on Ariana Grande's 2013 album Yours Truly. He also co-produced 5 songs on Yours Truly, in addition to the song "Last Christmas" from Grande's Christmas Kisses EP, as a member of production duo The Rascals. 
On September 24, 2013, Leon Thomas released a new single, "Hello How Are You", featuring Wiz Khalifa. A second single, "Chill," is to be released soon.
On January 1, 2014, Thomas released a new mixtape, V1bes, under the name Leon Thomas, via Datpiff. He also announced that a music video for his single, Hello How Are You, was in the works.
Thomas released a debut mixtape titled Metro Hearts on August 1, 2012. The song "Take Care" is originally performed by Rihanna and Drake. Thomas covered the song with his Victorious co-star, Ariana Grande.