In 1984, Tomita got her big break by traveling as Queen of Nisei Week to Hawaii when she was selected as part of a casting call by director John G. Avildsen to make her acting debut in The Karate Kid, Part II, playing Kumiko, the love interest of Ralph Macchio's character Daniel Larusso. She later had major roles in a number of independent movies. Her biggest role was in the 1990 drama film Come See the Paradise, which was written and directed by Alan Parker. In 1993 she co-starred opposite Ming-Na Wen in the ensemble cast drama The Joy Luck Cluband the next year she had a role in the 1994 independent film Picture Bride. In 1995 Tomita appeared alongside Antonio Banderas in the Robert Rodriguez directed segment in the vignette anthology comedy film Four Rooms.
In the new century Tomita has had roles in other independent films, and co-starred in several major Hollywood productions, including playing Janet Tokada - the climate scientist that teams up with climatology professor Jack Hall (Dennis Quaid) - in the Roland Emmerich directed 2004 disaster film The Day After Tomorrow. In 2005, she starred in the Brazilian drama film Gaijin 2: Love Me as I Am and also had leading roles in the independent films Robot Stories (2003) and Only the Brave (2006). Tomita also appeared in The Eye (2008) and Tekken (2009).