Mainetti was born in Rome, Italy, on August 8th, 1957. From the age of six to eighteen he studied classical guitar and, after High School, attended La Sapienza University in Rome (Political Science). He concurrently attended S.Cecilia and Licinio Refice Academy, where he obtained a degree in Music Composition in 1983. Simultaneously, he studied Orchestral Conduction, Orchestration and Counterpoint.

Specialized at the UCLA in California he attended national and international classic guitar competitions and was twice awarded Second Place at the internationally recognized Recanati Music Competition in Italy in both 1972 and 1973. Stefano Mainetti was awarded the "Oscar Giovanile" in Campidoglio, Rome 1983, for his piano performance of the popular RAI television show theme to "TG L'UNA".
He received the first place Italian Documentary Film Soundtrack Award for his having composed the music to “Ritorno alle Terme” (1987).

First Prize Agimus (Best Original Soundtrack) for the short movie "Sera" (1996). Winner (Best Original Soundtrack) at the Fantafestival in 1998 for "Tale of the Mummy" directed by Russel Mulchay.

Stefano Mainetti is one of the two composers who scored the Sony Classical CD "ABBA' PATER", which blends for the very first time Pope’s voices and chants with original music.

Represented by "DIBERTI & C." Mainetti is a member of S.I.A.E., the Italian musicians association. In 1995, he composed the soundtrack of the feature film “The Shooter” (1995), a Miramax Films by Ted Kotcheff (First Blood). In 1996, he composed the soundtrack of the feature film “Silent Trigger” starring Dolph Lundgren by Russel Mulcahy (Highlander). In 1997 he composed the music for "Sub Down" starring Stephen Baldwin.

In all, Stefano Mainetti has composed the musical scores for 27 films, 16 series, 64 documentary films, 20 stage productions as well as 30 CDs, the European television series "Eurocops" and the Italian television series "ORGOGLIO" (Pride). Best Music for Italian Fiction at the Ravello Festival 2005.
In 2006 and 2007 he is member of the commission of the "Festival di Sanremo".
"ANICA Prize" at the "Salerno Festival" in 2006 for the soundtrack of the TV movie
"A VOCE ALTA"
"Salvo Randone Prize" for the career in "Mazara del Vallo in 2007".
In the same year he has composed the music for "THE WORD OF PROMISE" a huge American audio drama of the New Testament in 20 cds with the voices of Jim Caviezel, Richard Dreyfuss, William Hurt, Louis Gossett Jr. and many others.