Mantovani was born in Venice, Italy and his father was the concertmaster of La Scala orchestra under Arturo Toscanini. His family moved to England in 1912, where he studied at Trinity College of Music in London. After graduation, he formed his own orchestra, which played in and around Birmingham. By the time World War II broke out, his orchestra was one of the most popular in UK, both on the BBC and in live performances.
He was also musical director for a large number of musicals and other plays, including ones by Noel Coward.