Born into a family of modest means at Volterra, Santi moved to Florence with his family when he was six years old. Apart from his brief sejourns in Rome, Milan and Paris, he lived in Florence all his life. He gained degrees in letters and jurisprudence, and worked for some years as a teacher. He started to wtite towards the end of the 1930s, initially as a critic of art and literature.

By the beginning of the 1940s he had become an indefatigable leader of cultural life in Florence. Among his many activities he founded an art gallery and directed a literary journal.

At last among his friends, Santi never hid his homosexuality. In the 1950s Santi published an autobiographical work which portraied the search, sometimes obsessive, for sexual partners in public places, such as on the banks of the Arno river ot at certain cinemas. Always fascinated by youth and beauty, Santi spent his final years surrounded by young and affectionate friends. He died in Florence.