Discovered by Funimation in 2005, Tatum was cast as Rikichi in Samurai 7. Tatum’s key roles include Kyoya Otori in Ouran High School Host Club, Sebastian Michaelis in Black Butler, Erwin Smith from Attack on Titan, Shu Tsukiyama in Tokyo Ghoul, France in the Hetalia franchise, Tomoe from Kamisama Kiss, and the equal parts maniacal/vulnerable Rintaro Okabe from Steins;Gate. More recently, Tatum can be heard in the epic My Hero Academia as Teyna Iida.

Some of his other characters include Doumeki in XXXHolic, Jiro Mochizuki in Black Blood Brothers, Isaac Dian in Baccano!, both God Eneru and Dalton in One Piece, Komui Lee in D-Gray Man, Dororo in Sgt. Frog, the titular loveable savage of Heroic Age, Ryosuke Takahashi in Initial D, Lawrence Kraft in Spice and Wolf, Zarbon in Dragon Ball Z Kai, and Scar in Full Metal Alchemist: Brotherhood.

He has also been featured in Romeo X Juliet, Speed Grapher, Trinity Blood, Kenichi: The Mightiest Disciple, Black Cat, Nabari no Ou, Ghost Hunt, School Rumble, The Tower of Druaga, Aquarion, Tsubasa: Reservoir Chronicles, Shuffle, Shigurui, Glass Fleet, Mushishi, Soul Eater, along with feature-length films such as Vexille, Summer Wars, Dragon Age: Dawn of the Seeker, and Empire of Corpses, among many others.