Adeodato Giovanni Piazza was born in Vigo di Cadore, a small town of the Veneto, and was ordained a priest of the Order of Discalced Carmelites in 1908. In 1930 he was ordained a bishop and appointed as Archbishop of Benevento, Italy.
He was appointed Patriarch of Venice in December 1935 and was formally installed as patriarch early the next year. He was elevated to Cardinal by Pope Pius XI in the consistory of 13 December 1937 with the title of Cardinal-Priest of Santa Prisca. As Cardinal, Piazza participated in the Papal conlave that elected Pope Pius XII.
Cardinal Piazza remained Patriarch of Venice until 1948 at which time he was named Secretary of the Sacred Consistorial Congregation (now called the Congregation for Bishops) by Pius XII. He remained in this capacity until his death.
In 1949 his title was changed by Pius XII to Cardinal-Bishop of Sabina e Poggio Mirteto.