His deep voice and keen sense of timing earned him numerous radio drama roles during the 1950s, and later in the Channel 7 telenovela series, La tarde de Palmolive.

Returning to Argentina, he appeared in Fernando Ayala's adaptation of historian Félix Luna's historical drama, Argentino hasta la muerte (1971), and directed the picaresque comedy Autocine mon amour (1972).

He directed numerous comedies and musical films, which became popular in Argentina during the troubled 1970s, and would star in a number of these, notably with Jorge Porcel in Te rompo el rating (1981), and in Alejandro Azzano's tragicomic Venido a menos (1981).

[1] Siro was also active in the theatre, playing over 60 roles in his career, notably in Leo Tolstoi's Anna Karenina, Jean-Paul Sartre's The Respectful Prostitute, Tennessee Williams' A Streetcar Named Desire, Arthur Miller's A View From the Bridge, and Ken Ludwig's Lend Me a Tenor.

Their decision to join a small rally on March 24, 2001, in support of the former dictator in power during the height of the Dirty War, General Jorge Videla, led to their expulsion from the Argentine Actors Association.