After graduating from Saitama Prefectural Urawa High School, Tomita entered Nippon University College of Art with the goal of becoming a lighting staff for live action films. However, he failed to receive adequate lessons on that field due to conflicts with his schedule at the university. He eventually tried his hand at writing plays and parodies, which got him positive responses from his peers, so he turned to his desire of becoming a screenwriter.
After graduation, he worked at a screenwriter's office, but spent most of his time doing tedious managerial work rather than actual screenwriting. Frustrated, he took a break before being encouraged by fellow Toei staffers to try writing again, this time under the tutelage of senior writer Tatsuo Tamura who had worked on television series such as UFO Robo Grendizer and Getter Robo. In 1978, after three years of training, he made his debut working on the fourth episode of Starzinger. From there, he would go on to work on other high profile projects such as Space Runaway Ideon and eventually, the Super Dimension Fortress Macross television series. He also wrote tie-in material such as Misa Hayase: White Reminiscences. He then would work on The Super Dimension Fortress Macross: Do You Remember Love? and Super Dimensional Fortress Macross II: Lovers Again OVA. Other notable works he worked on art Genesis Climber MOSPEADA, Fang of the Sun Dougram, Heavy Metal L-Gaim and Aura Battler Dunbine.