Martin made her television debut in 2006, with the television pilot Cooking Rocks! It was followed by roles in programs such as Nickelodeon’s Just Jordan and CBS’s Close to Home, as well as a guest stint in the Disney Channel series The Suite Life of Zack & Cody. She was eventually cast as the lead antagonist in the Disney Channel original movie, Camp Rock, which also stars Demi Lovato and the Jonas Brothers.

Martin was selected by TV Guide in 2008 as one of the “13 Hottest Young Stars to Watch”. She was the online host for the 2008 Disney Channel Games.

Martin voiced the character Naminé in all subsequent releases in Kingdom Hearts series, replacing Brittany Snow, who did not return to the series.

Martin starred in the ABC Family sitcom 10 Things I Hate About You as Bianca (originated by Larisa Oleynik in the film version). She also had the role of Megan Kennedy in the independent film Dear Lemon Lima. Martin filmed the sequel to Camp Rock, Camp Rock 2: The Final Jam, reprising her role as Tess Tyler, which was released on September 3, 2010 on Disney Channel. It was announced that Martin will star in the upcoming film Mean Girls 2. It will be the sequel to the 2004 film, Mean Girls.