Guiso was born on April 15, 1956, in Rome, Italy, which had been the capital of the Italian state since the Kingdom of Italy took the city in 1870. The change also made the city's ancient university the main university of the new capital, which led to its rapid expansion in the decades that followed.
Guiso's legal education was at the University of Rome, where his law studies are recorded as ending in 1980.
The institution was founded in 1303 by papal decree as a centre of ecclesiastical study. In 1431 Pope Eugene IV reorganized it to include law, medicine and philosophy alongside theology. After 1870 it served the capital of unified Italy, and its main campus, planned by Marcello Piacentini, was completed in 1935.
Admission to the Italian bar follows legal training and a state examination. Guiso was admitted in 1983, three years after his law studies at the university ended.
Guiso was admitted to the bar in Italy in 1983.
He later became a partner of Studio Legale Ardito. The name is associated with a firm founded in Milan in 1981 by the lawyer Mauro Ardito, which works in labour, civil and corporate law and collaborates with a network of legal and tax professionals in Italy and abroad.
A former partner of Studio Legale Ardito later described the firm as having offices in Rome, Milan and London.
