Graham made his acting debut in sitcom The King of Queens in 2002 as the character Winthrop in the epsisode "Mentalo Case". In 2004, he appeared as as Toby Carroll in the show Judging Amy in the episode "Legacy". He made his film debut in the movie Noel, playing the part Boy Soprano. The following year, he guest starred in Love's Long Journey as Jeff Huff. He continued to act, gaining roles in Crossing Jordan as Jonah Wheeler/Kyle. In 2007, he appeared in The Ten Commandments: The Musical as Moses' Son and as Jordan Baxter in the blockbuster Evan Almighty for which he was nominated for a Young Artist Award for Best Performance by a Supporting Young Actor in a Feature Film - Comedy or Musical. He eventually landed the lead role as Ben Tennyson in Ben 10: Race Against Time, the live-action adaption of the animated series which earned him a Young Artist Award nomination for Best Performance by a Leading Young Actor ina TV Movie, Miniseries, or Special. In 2008, he starred as Evan Goldman, the main character, of the coming-of-age Broadway musical, 13. Since 2009, he has portrayed the character Zach Florrick on the drama The Good Wife for which he has recieved three Screen Actor Guild Awards for Outstanding Performance by an Ensemble Cast in a Drama Series, and one Young Artist Award nomination for Best Supporting Young Actor in a TV Series - Comedy or Drama.
He dated 13 costar Ariana Grande from 2008 until December 2011.