Martin made her acting 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. Martin eventually cast as the lead antagonist Tess Tyler in the Disney Channel original movie, Camp Rock, starring 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 recorded two songs in Camp Rock, "Too Cool" and "2 Stars". Martin sang a version of "When You Wish Upon a Star" for the 2009 re-release of Disney's Pinocchio, as well as appearing in the related music video. The song debuted at number fifty-two on Billboard's Hot Dance Club Songs chart, becoming her first and only chart single. It has since peaked at number thirty-seven.
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 returned to reprise her role as Tess Tyler in Camp Rock 2: The Final Jam, premiered on September 3, 2010 on Disney Channel. In 2011, Martin played the main character Jo in the television film Mean Girls 2, the sequel of the 2004 film Mean Girls. Martin also played the role of Aubrey in the film Sironia.
On June 16, 2011, Martin appeared for one night in Super Summer Theatre's live production of "Annie" at Spring Mountain Ranch in Las Vegas, Nevada in the role of Star-To-Be. Martin is also starring in Wendy (web series) as Wendy alongside Tyler Blackburn. Wendy is a dark twist on 'Peter Pan'. The series premiered on macys.com on September 15, 2011. In 2013, Martin appeared in the film adaptation Geography Club as Trish, while she appeared in the thriller The Good Mother was aired on Lifetime Channel. Martin voiced the character of Jessica in the PlayStation 4 exclusive Until Dawn.
Martin became engaged to British actor Oli Higginson in May 2016. They were married on September 24, 2016 in London, UK.
