|Died||July 26, 1995|
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He was born in Premilcuore, Italy and educated at the Russicum, a Jesuit seminary established to prepare Catholic priests for missionary work in Russia. In 1941 Leoni went along with an Italian regiment aiding the German invasion of the USSR. In 1943 he was released from service as the Italian army disintegrated and he decided to stay on as a priest in Odessa. On April 29, 1945 he was arrested for counter-revolutionary activity for which was sentenced to 25 years in forced labor camps but was released in 1955 through intervention of the Vatican. Following his return to the West, Leoni served as pastor of the Russian Catholic community in Montreal, where he died on July 26, 1995.
- Sergey Golovanov. "The Historical Destiny of the Russian Catholic Tradition of the Byzantine Rite, 1917 – 1991." Archived 2009-12-26 at the Wayback Machine
- "Mission in the Night," Time Magazine, June 13, 1955
- Elena Dundovich, Francesca Gori, and Emanuela Guercetti (2003). Reflections on the Gulag: With a Documentary Index on the Italian Victims of Repression in the USSR. Feltrinelli Editore. ISBN 978-88-07-99058-8.
- Methodios Stadnik. "Nec Plus, Nec Minus, Nec Aliter: A Brief History of the Russian Byzantine Catholic Church and the Russian Catholics."