The purpose of the Archives of the Diocese of St. Petersburg is to collect, preserve, and make available for research the official records of the Diocese and those ancillary records which reflect the work of the Catholic Church within the Diocese. The Archives is erected in accordance with Canon 482, which charges the Chancellor with the responsibility for the Archives.

The Diocesan Archives seeks to promote an understanding of the origins, aims, and goals of the Diocese as reflected in the workings of the official Diocesan agencies, institutions, and offices. Official diocesan records are defined as:

all recorded information, regardless of media type or characteristics, made or received and maintained by an agency, institution or office of the Diocese of St Petersburg in pursuance of its legal obligations or in the transaction of its business.

The Diocesan Archives also seeks to collect, preserve, and make available for research those records of individuals and organizations engaged in work which is reflective of the work of the Catholic Church in the Diocese of St. Petersburg. Such individuals and organizations may operate within the Diocese in an adversarial capacity, as a unit supervised by the Diocese or as an advocate of the Diocese.