Giannini's parents were Italian immigrants to the United States. Giannini opened the Bank of Italy in a former San Francisco, California saloon on 17 October, 1904. Deposits on that first day totaled $8,780. An early difficulty to overcome was the San Francisco earthquake of 1906. Giannini was forced to run his bank from a plank in the street for a time.
By 1916 Giannini had expanded and opened several other branches. It became the Bank of America in 1928 and continued under Giannini's chairmanship until his retirement in 1963.