Ordained to the priesthood in 1946, Father Ossanno exercised his ministry in Padua and Paris before joining the faculty of the Seraphicum in 1977.
In 1979—the first full year of St. John Paul II’s pontificate — Father Ossanno preached the Lenten spiritual exercises to the Roman Curia.
Ten years later, the Pope named him apostolic examiner of the Roman clergy.