The community of St. Leonard was founded in 1968. The first mass was celebrated on October 13, 1968 by Father John Meenderink, SCJ, in the gymnasium of St. Leonard Elementary School, which had been built in 1965. His successors were Father Leo Hermans, SCJ, in 1971 and Father Joe Eliens, SCJ in 1977. They were assisted by Father Adrian Visscher, SCJ, Father John Vanden Hengel, SCJ, and Father Bill DeWitte, SCJ. These Sacred Heart Fathers served the communities on a full-time basis from 1960 to 1979.
As the community grew, the parishioners prayed that one day they would have a Church of their own in Manotick. The Church of St. Leonard on the Rideau River was constructed during 1980-1981, beginning with a sod-turning ceremony on October 18, 1980. The official opening occurred on June 21, 1981 under the pastorship of Father James Whalen, who served the parish from 1979 to 1984.
Father Tom Riopelle was assigned to St. Leonard from 1984 to 1989. Father Riopelle requested independent status from St. John the Evangelist and St. Brigid Churches on June 13, 1988. The Council of Priests gave its approval to that request at a meeting on June 22, 1988. St. Leonard was given independent status in Ottawa at the Metropolitan Curia, on September 15, 1988 and took effect on September 25, 1988.