Guido Ajmone-Marsan was born in Turin and is now an American citizen living in London. Having studied at the Eastman School of Music and with Franco Ferrara at the Santa Cecilia Conservatory in Rome, he was 1st prize-winner of the Rupert Foundation Competition (including a one year assistantship with the London Symphony Orchestra in 1973) and the Georg Solti Prize (Chicago 1973).
Following these competitions he appeared as guest conductor with many prestigious orchestras including the Chicago Symphony, Cleveland Orchestra, Philadelphia Orchestra, San Francisco Symphony, London Symphony, Philharmonia, Royal Philharmonic, BBC Symphony, Orchestre de Paris, Tonhalle-Orchester Zürich, Orchestra dell'Accademia Nazionale di Santa Cecilia, Orchestra Filharmonica della Scala, all the major German radio orchestras, the Royal Danish Orchestra, the Royal Stockholm Philharmonic Orchestra, the NHK Symphony and the Sydney and Melbourne Symphony Orchestras.
His operatic debut in 1976 at the Festival dei due Mondi in Spoleto started a long career in many of the world's most illustrious opera houses including the Metropolitan Opera, Royal Opera House, Covent Garden, San Francisco Opera, New York City Opera, English National Opera, Scottish Opera, Welsh National Opera, Teatro Colon, Buenos Aires, Teatro Municipal, Santiago and the Deutsche Oper, Berlin. In addition he served as conductor for the Cardiff Singer of the World competition from 1991 - 1995.
From 1982 - 1986 he was Principal Conductor of the Gelders Orkest in Arnhem, 1983 - 1988 Chief Conductor of the Orchestra of Illinois (Chicago), and from 1986 - 1990 Opera Director in Essen.
In addition to the standard Italian operatic repertoire of the 19th century, he has performed such works as L'heure espagnole, L'enfant et les sortilèges, Hänsel und Gretel, Der fliegende Holländer, Die Walküre, Götterdämmerung, La fanciulla del West, La navarraise, La rondine, La Wally, Andrea Chenier, Dead Man Walking, Prince Igor, Salome, Ariadne auf Naxos, Boris Godunov, Mireille, Béatrice et Bénédict, The Queen of Spades and Attila.