Gillies reprised her role as Jade in a special episode of the i Carly and Victorious spinoff series Sam and Cat. During her time on Victorious, Gillies lent her talents to other Nickelodeon shows, voicing the character of Daphne on the animated series Winx Club and recording Winx Club's official song, "We Are Believix." She also appeared in an episode of Big Time Rush and as a contestant on game shows Brain Surge and Figure It Out.Beginning in 2012, Gillies began playing small guest roles outside of Nickelodeon.In 2013, she was cast as Courtney in the musical adaptation of Jawbreaker and participated in a reading of the show in Manhattan.
In the summer of 2008, Gillies was cast as Lucy in a Godspeed production of Jason Robert Brown's new musical 13, alongside her future Victorious co-star, Ariana Grande.
Later that year, 13 moved to Broadway, which made it the first Broadway production to have a cast and band entirely made up of teenagers.
Regarding her Victorious character, Gillies said "It’s wonderful. I always say she’s not so much the “mean” girl, but the “bad” girl in so many ways.
She has a lot of human qualities to her — she’s not just completely sociopathic. It’s nice to play a character with some depth." The show premiered on March 27, 2010, and ended on February 2, 2013 after four seasons.
Her first television role was as a recurring character in The Black Donnellys.