Osvaldo Valenti was born in Constantinople, Ottoman Empire (present-day Turkey), to a Sicilian carpet trader and a wealthy Lebanese woman of Greek descent.

[2] Two years later, he left the university and went to live first in Paris and then in Berlin, where he made his acting debut with a supporting role in the German silent drama film Hungarian Rhapsody, directed by Hanns Schwarz (1928).

At the beginning of the 1930s, he returned to Italy and worked with film directors Mario Bonnard (Five to Nil, 1932) and Amleto Palermi (La fortuna di Zanze, 1933 and Creatures of the Night, 1934).

[2] After the fall of the Fascist regime in 1943, Valenti joined the Republic of Salò, and moved to Venice together with his mistress Luisa Ferida, renouncing a contract for two films to be shot in Spain in early 1944.

In April 1944, Osvaldo joined, with the rank of lieutenant, the Decima Flottiglia MAS, an elite commando unit led by Junio Valerio Borghese.