Saint Leonhard's International English-Speaking Roman Catholic Parish was officially established as an active parish of the Diocese of Limburg on 1st December 1995. It evolved from the US military parish of St. Sebastian's, which closed in January 1995 after 47 years with the departure of the US Army from its Frankfurt facilities. St. Sebastian's parishioners arranged with the Diocese of Limburg for a permanent home for the English-speaking Catholic community in Frankfurt. Luckily the beautiful church of St. Leonhard was available at the time. It is the oldest parish church in Frankfurt, dating back to the 13th century.
The then-Bishop Franz Kamphaus recognized the need for English speakers to worship in their language, irrespective of nationality. He established a "missio cum cura anumarum", an international parish community without restricted territorial boundaries but serving Roman Catholics in the Frankfurt area who share English as their common language.