Saint Leonhard's International English-Speaking Roman Catholic Parish was officially established as an active parish of the Diocese of Limburg on December 1, 1995. It evolved from the U.S. military parish of St. Sebastian's, which closed in January 1995 after 47 years with the departure of the U.S. 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 in the historic center of the city was available at the time. It is the oldest parish church in Frankfurt, dating back to the 13th century.
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.
During a major, long-term construction project to restore the historic St. Leonhard's building, the parish found a home at Holy Cross Center for Christian Meditation and Spirituality in Frankfurt's Bornheim district, and that church, dating from the late 1920s, remained the site for Sunday morning Masses, with the city-center location becoming the venue for Saturday Vigil Masses when it reopened in November 2019. In January 2020, the parish was merged with the English-language parish of St. Mary's in the neighboring town of Liederbach.