Saito has appeared in numerous stage productions, with early career work at the Asian American theatre company East West Players in Los Angeles. On Broadway he has appeared in The King and I, and David Henry Hwang's Golden Child. He won an Obie Award in 2007 for his performance in Julia Cho's Durango at The Public Theater in New York City.
In 2008, he played Tokugawa Ieyasu in Shogun, as part of the BBC's Heroes and Villains series, (focusing on historical people who have attracted polarized opinion, in modern day, or by their contemporaries.) It is probably the role he is best known for to British Audiences, his performance as "the Caesar of Japan" (Hideyoshi is considered the Napoleon) was well received by audiences.
In 2015, Saito appeared in a new play, The World of Extreme Happiness, by Frances Ya-Chu Cowhig, in a co-production with the Goodman Theatre at the Manhattan Theatre Club in New York City.
Saito starred in the regular supporting role of Dr. Chen in the ABC drama Eli Stone. In 2017, it was announced that he would have a recurring role in the Marvel series Cloak and Dagger.
