Born to parents from two of Iran's aristocratic families, Mansouri was named "Lotfollah" (meaning "kindness of God") after he was pronounced dead at birth and then was unexpectedly revived. From early childhood, he felt an attraction to Western music and culture.

His father intended that his son become a doctor, and although not inclined to study medicine, he agreed to follow his father's wishes with the provision that he be allowed to attend UCLA. Possessing a promising tenor voice, he soon found himself pursuing musical studies, however, to the neglect of his pre-med coursework. He was recruited by Irving Beckman, director of the UCLA Opera Workshop, to appear in a musical presentation opposite Carol Burnett.