Gentilomo came even during his school days to Rome and worked as a set designer before turning to film. In this profession, he started as a production manager and assistant editor for eg Nunzio Malasomma and Gennaro Righelli, and later as an assistant director for Carlo Ludovico Bragaglia. In 1939 he finally made his first film as a director, after he had two years earlier the first short film that used the Technicolor process in Italy staged. In 1945 he published the remarkable O sole mio, which blended elements of neorealism with the Neapolitan elements. Until 1963 he made quite a few genre films, often melodramas; after completion of this career, he turned to painting.