The Basilica of Saint Mary was commissioned by Archbishop Ireland (1838-1918) and designed by French architect Emmanuel Masqueray (1861-1917) in a beaux-arts style. It was intended to house the relocated parish of the Immaculate Conception, founded in 1868.
The building was constructed between 1907-1915. Interior work, begun in 1922, was near completion when Pope Pius XI named the church the first Basilica in the United States on February 1, 1926.
The marble altar and baldachin (the canopy over the altar) were designed by Boston architects Maginnis & Walsh, and handcrafted at the Benziger Brothers Studios in Pietrasanta, Italy. Monsignor Reardon describes his vision for the altar in his history of the Basilica: "In finishing the church the major problem was, of course, the main altar. On its solution everything else depended; for the altar would give meaning and tone to all the rest... For that, the finest marble that money could procure must be available, and the most skillful sculptors commissioned to chisel it into life... The altar must be one of the finest in America in material, design and workmanship."