Born in the Bronx, New York, he made his Broadway debut in the original production of the musical South Pacific in 1949.
[1] Prior to that he spent six months in England playing the role of "Stefanowski" in the London company of Mister Roberts, which starred Tyrone Power.
[citation needed] While studying with Erwin Piscator at the Dramatic Workshop of The New School for Social Research, he was seen in 'The Flies,' 'There is No End,' and 'Crew 55' (sourced from the original theatre program for 'South Pacific', 1949.)
Sidney played the character of "Itchy" Flexner, the social director, in the Broadway production of the musical comedy Wish You Were Here[2] which opened at the Imperial Theatre on June 25, 1952, and closed on November 28, 1953, after 598 performances.
In films, Armus had roles in Sleepless in Seattle, One Fine Day, Postcards from the Edge, and The Thomas Crown Affair.