Andre Bessette joined the Congregation of Holy Cross in 1870 and spent years as the doorkeeper at Notre Dame College in Montreal. Sickly and barely literate, he was an unlikely figure to become internationally renowned, yet pilgrims began seeking him out for healings attributed to his devotion to Saint Joseph. By 1904, the Congregation gave him funding to construct a small Gothic Revival chapel on Mount Royal, directly across from the college. The chapel expanded four times over the next decade as Bessette's fame grew. The original structure, now relocated about a hundred meters from its original site, still stands -- a miniature wooden reminder of the scale of what came after. The Congregation decided to fulfill Bessette's dream of a full basilica. He would not live to see it completed; he died in 1937, when the dome was just beginning to rise. He was canonized as a saint in 2010.

The basilica's construction reads like a relay race across generations of architects. Dalbe Viau and Alphonse Venne began the crypt church between 1914 and 1916, seating 1,000 worshippers beneath barrel-vaulted ceilings of steel-reinforced concrete. Between 1924 and 1927, they raised the structure to the roofline in the Renaissance Revival style, envisioning a dome modeled on St. Peter's Basilica in Rome. Then the Great Depression halted everything. When work resumed in 1937, the French architect Dom Paul Bellot was hired, but since he was not licensed in Quebec, he was required to work through the Canadian architect Lucien Parent. Bellot threw out the original dome plans entirely. He redesigned it to echo Florence Cathedral instead, making it significantly larger than Viau and Venne had imagined. Thousands of workers labored for four years, and the dome was completed in 1941. Architect Gilbert Moreau carried out further interior alterations between 1949 and 1951. The building that stands today is the product of at least five architects across six decades.

The Oratory's architecture is a study in deliberate tension. Its exterior presents a monumental Renaissance Revival facade -- classical columns, symmetrical proportions, the massive dome rising above the mountain. Step inside, and the mood shifts to Art Deco: geometric forms, clean lines, and a modernist sensibility that would have been radical for a church in the mid-20th century. The basilica comprises several distinct spaces. The Crypt Church, embedded in the mountain beneath the main basilica, holds a Carrara marble statue of Joseph by the Italian artist A. Giacomini, installed in 1917, and eight stained glass windows depicting the stages of Saint Joseph's life. The Votive Chapel, designed by Lucien Parent and built between 1946 and 1949, glows with approximately 10,000 candles and holds nearly 1,000 ex-votos -- canes and crutches left behind by pilgrims who visited Brother Andre during his lifetime. His tomb, sculpted in black marble, rests in an alcove at the chapel's center.

Montreal's municipal building code forbids any structure from exceeding the height of Mount Royal. The Oratory is the sole exception. Its dome is the largest church dome in Canada and the third largest in the world, a distinction that makes the building visible from vast distances across the city. More than two million visitors and pilgrims climb the 283 steps each year, some ascending on their knees in acts of devotion. Since 2018, a C$80 million renovation project led by architecture firms Atelier TAG and Architecture49 has been renovating the dome and its lantern, with plans to create a 360-degree observation platform -- the only such viewpoint over the mountain in the entire city. On April 8, 2024, thousands of people filled the steps and surrounding grounds to watch a total solar eclipse, witnessing 85 seconds of totality as Venus and Jupiter appeared in the darkened sky. It was the kind of spectacle the Oratory was built for: a place where the monumental and the intimate meet on the slopes of a mountain.