He was once the national teenage spokesperson for Greenpeace. He has also written a novel called The Warrior.
He is also widely known to Disney fans for providing the voice of Prince Eric in Disney's 1989 animated film The Little Mermaid, and reprised the role again in the video game, Kingdom Hearts II. He was only 16 years old when he first provided the voice, but the producers cast him because he sounded much older. This probably made him the youngest actor to voice a Disney Prince. Barnes also provided the voice for Prince Charming in Cinderella II: Dreams Come True and Cinderella III: A Twist in Time and Electro in Ultimate Spider-Man.
He appeared as a student in The Golden Girls season 6 episode "Feelings".