By 1824 the congregation had completely outgrown the church, and James O'Donnell, an Irish-American Protestant from New York, was commissioned to design the new building. O'Donnell was a proponent of the Gothic Revival architectural movement, and designed the church as such. He is the only person buried in the church's crypt. O'Donnell converted to Catholicism on his deathbed perhaps due to the realization that he might not be allowed to be buried in his beautiful church. It also has a Casavant Frères pipe organ, which comprises four keyboards, 97 stops, almost 7000 individual pipes and a pedal board

The sanctuary was finished in 1830, and the first tower in 1843. On its completion, the church was the largest in North America. The interior took much longer, and Victor Bourgeau, who also worked on Montreal's Mary, Queen of the World Cathedral, worked on it from 1872 to 1879. Stonemason John Redpath was a major participant in the construction of the Basilica. Because of the splendour and grand scale of the church, a more intimate chapel, Chapelle du Sacré-Coeur (Chapel of the Sacred Heart), was built behind it, along with some offices and a sacristy. It was completed in 1888.

Notre-Dame Church was raised to the status of basilica by Pope John Paul II during a visit to the city on April 21, 1982. The basilica now charges a $4.00 entry fee for visitors, unless they are there to attend mass. "And Then There Was Light," a sound and light show detailing the history of the church, is also offered in the evening, Tuesday through Saturday (tickets are $10 for adults [18+], $9 for seniors, and $5 for children and young adults).