Tomasi was born in Palermo to Giulio Maria Tomasi, Prince of Lampedusa and Duke of Palma di Montechiaro, and Beatrice Mastrogiovanni Tasca Filangieri di Cutò. He became an only child after the death (from diphtheria) of his sister. He was very close to his mother, a strong personality who influenced him a great deal, especially because his father was rather cold and detached. As a child he studied in their grand house in Palermo with a tutor (including the subjects of literature and English), with his mother (who taught him French), and with a grandmother who read him the novels of Emilio Salgari. In the little theater of the house in Santa Margherita di Belice, where he spent long vacations, he first saw a performance of Shakespeare's Hamlet, performed by a company of travelling players. His cousin was Fulco di Verdura.