Born in Gries am Brenner, Tyrol, Moretti is the oldest of four brothers. His brothers are named Tomas, Cristoph and Gregor. Since 1997 he has been married to Julia Moretti (born Wilhem), an oboist. They have two children, Antonia (born August 1998) and Lenz Valentino (born February 2000). The name comes from her mother, who is an Italian.
Moretti studied composition at the Vienna University of Music and Applied Arts, then went to Munich to train for the stage at the renowned Otto-Falckenberg Schule. After graduation he was a permanent member of the Bayrische Staatsschauspiel ensemble (Frank Baumbauer) and played at the Munich Kammerspiele (Dieter Dorn) from 1985 to 1995 where he earned critical praise in a sweeping variety of productions, appearing in Bertolt Brecht's Man is Man, Achternbusch's Der Frosch (The Frog) and playing the lead in Shakespeare's Troilus and Cressida.
