The purpose of the Archives of the Archdiocese of Ottawa-Cornwall is to collect, organize, preserve, and make available for research the historical and vital records of the Archdiocese, as well as the records of individuals and organizations whose work reflects the work of the Catholic Church within the Archdiocese.

The Archives of the Archdiocese of Ottawa-Cornwall is also the continuation of the social and built history of Eastern Ontario. Therefore, some older records relating to the Outaouais and Laurentides regions of Quebec are part of the collection.