Born in California, Soo spent several years of his young adulthood during WWII in an internment camp in Utah along with many other US citizens of Japanese descent. After the war he did standup comedy on a nightclub circuit in the Midwest and befriended another performer, Danny Arnold, who would eventually produce "Barney Miller". Soo's breakthrough came when he played Sammy Fong, one of the four romantic leads and a kind of "Chinese Nathan Detroit" as "Variety" put it, in the Rodgers and Hammerstein Broadway musical "Flower Drum Song" (1958). In 1961 Soo made his film debut recreating the role, and over the next decade acted in several other films. He played a colonel in John Wayne's controversial pro-Vietnam War "The Green Berets" (1968) and threw Mary Tyler Moore into a clothes hamper as Bea Lillie's cartoonish henchman in "Thoroughly Modern Millie" (1967).
Already tending to play ambling ne'er-do-wells, Soo first ventured into TV series work as the poker-playing ex-Army buddy turned con-artist valet to debonair publishing executive Valentine Farrow (Anthony Franciosa) on the sitcom "Valentine's Day" (ABC, 1964-65). Soo's career had its dry spells, during which he made several TV-movies and played a recurring role on "The Jimmy Stewart Show" (NBC, 1971-72), but "Barney Miller" (ABC), beginning in 1975, insured his niche in popular memory four years before his death from cancer. Forever making bad coffee, griping to his bookie on the phone and moseying about offering sardonic Greek chorus-style commentary on the suspects hauled into the precinct, Sgt. Yemana finally offered full scope to Soo's quietly engaging but nonetheless formidable comic prowess.