In November 1930, English-speaking parishioners of Notre-Dame-de-Lourdes submitted a petition to their bishop, requesting that a parish be established with full-time priests speaking their own language. The new church was to be built in the western part of the existing parish. They also hoped to attract French-speaking parishioners who lived far from Notre-Dame-de-Lourdes, as this would help finance the construction of their new church.

In fact, the establishment of such a parish represented for the community of Notre-Dame-de-Lourdes a very real possibility that one quarter of its parishioners would transfer their allegiance to the new parish, and the resulting loss in revenue would be significant.

However, French-speaking parishioners were not prepared to throw in the towel. They asked the bishop to grant them permission to build a chapel near the church for English-speaking parishioners. The Montfortain Fathers of the mother church would take charge of religious services in the chapel.

Mgr. Forbes granted the requests of both language groups, and that is how Assumption Parish and Marie-Médiatrice Chapel were established. The chapel was built on Third Avenue (now Cyr Street) in 1931.

During the following year, however, the parishioners who attended the chapel asked to be autonomous. After prolonged negotiations between the Montfortain Fathers and the archbishop, the parishioners of Marie-Médiatrice opened their own church, located at 344 Cyr Street, in November of 1960.

Wishing to establish a house of worship for itself, the Burundi community of Ottawa has now become associated with the parish of Marie-Médiatrice.