St. Margaret's was the third parish to be created in response to the needs of a growing population in the residential area of Brent Park in Port Arthur and as a relief to the increasing demands placed on St. Andrew's Church. The construction and opening of St. Margaret's Roman Catholic School on Clayte Street in 1954 prompted Bishop Jennings to investigate the purchase of property owned by the Sisters of St. Joseph adjacent to the school. "It would make another very fine little Catholic corner of Port Arthur" wrote Bishop Jennings, "considering that there is such a splendid school already there". The Fort William Diocese purchased one acre across from the school and, until a church could be built on the property, Sunday and some weekday masses and services, conducted by the Jesuits at St. Andrew's were held at St. Margaret's School. In March 1957 Bishop Jennings blessed and dedicated a new church on the property to be known as St. Margaret's chapel-of-ease "to provide a convenient centre of worship for the more distant members of the already larger than capacity congregation of St. Andrew's". Four years later, the chapel-of-ease was elevated to the status of a full-fledged parish with Father J.E. Roenicke as its first pastor.