Pietro Boetto was born in Vigone to Antonio and Caterina (née Anghilano) Boetto. One of two brothers and three sisters, he was confirmed by Bishop Filippo Chiesa of Pinerolo in 1883. Boetto attended the diocesan seminary of Giaveno from 1884 to 1888, when he entered the Society of Jesus on February 1. While studying at the novitiate in Chieri, he took his first vows on September 8, 1890. In 1901, he was ordained to the subdiaconate (July 28), diaconate (July 29), and finally priesthood (by Bishop Emiliano Manacorda on July 30). After finishing his studies in theology in 1902, Boetto then served as a professor and the rector of the Genoese “Istituto Arecco” until 1904. He took his final vows as a Jesuit on February 2, 1906, whilst serving as rector of St. Thomas College in Cuneo (1905–1907). From 1907 to 1916, he was procurator of the Jesuit residence in Turin. Boetto was provincial of the Jesuit Province of Turin before going to Spain to serve as visitor to the Jesuit Provinces of Aragón (1919–1920) and later of Castilla (1920–1921). He also served as Procurator General of the Society of Jesus (1921–1928), provincial of the Roman Province (1928–1930), and Assistant to Italy (1930–1935).

Pope Pius XI created Boetto Cardinal Deacon of Sant’Angelo in Pescheria in the consistory of December 16, 1935. On March 17, 1938, he was appointed Archbishop of Genoa. Boetto opted to become a Cardinal Priest (with the same titular church), a day after his appointment to Genoa, on March 18. He received his episcopal consecration on the following April 24, 1938 from Cardinal Gennaro Pignatelli di Belmonte, with Archbishops Giuseppe Migone and Giovanni Vallega serving as co-consecrators, in the church of Sant’Ignazio. Pietro Boetto was one of the cardinal electors who participated in the 1939 papal conclave, which selected Pope Pius XII. During World War II, he was a staunch defender of Genoa and its citizens. He protested against the shelling of the city by British warships, claiming God would assure the triumph of Italy. On December 8, 1945, Genoa awarded its Cardinal with citizenship after he urged all Axis forces near the city into surrender. Pietro Boetto died from a heart attack at 1:30 a.m. in his archiepiscopal residence, at age 74. His Requiem Mass was celebrated five days later, on February 4, 1946, by Bishop Pasquale Righetti at San Lorenzo Cathedral; Bishop Giuseppe Siri, the auxiliary of Genoa, delivered the funeral oration. Boetto was finally buried in the crypt near the main altar of that same cathedral of Genoa.