At the age of 13 he was discovered by the tragedian actor Tommaso Salvini while partaking in a charity performance.

As a sideline, he taught acting, among his pupils were Ida Lupino, June Duprez and his son Bobby.

Rietti had a major success in the live television production of To Live in Peace (1951), playing the lead role, the lovable priest Don Geronimo Bonaparte, uncle of Napoleon - a part he previously played on the stage in one of his own productions.

He had personally translated the Italian play by Giovacchino Forzano and adapted it for television.

Due to popular demand, To Live in Peace was re-staged for television in early 1952 (BBC), 1956 (RAI), and again in 1957 (BBC), and was broadcast for radio as well in 1953 and 1956 with Rietti repeating his performance in all six productions, and his son Robert playing the part of Maso.

Rietti's television success with To Live in Peace led to his touring internationally with the play for Ralph Reader.

Producer Sydney Box planned a motion picture of the play starring Rietti which never evolved.

For American television he guest starred with his son Robert Rietty in The Jack Benny Program (1957) in which he played two roles, and Harry's Girls (1963), both directed by his friend Ralph Levy.