In 1942, Willmann entered the Manila San Jose Seminary as a teacher in Social Sciences. He became treasurer of the seminary in 1948. He taught at the seminary until 1951. Willmann became a prisoner of war during the Japanese occupation of Manila where he was arrested at the University of Santo Tomas by the Japanese in July 1944. He and the other prisoners where later put into a concentration camp in Los Banos, Laguna and was later freed by American forces in 1945. On July 1, 1975, Willmann was granted Filipino citizenship by then President Ferdinand Marcos through Presidential Decree No. 740 for his "virtuous acts, compassionate and kind and loving service for the Filipino people,". On June 29, 1977, Pope Paul VI awarded Willmann the Pro Ecclesia et Pontifice medal, the highest award the Pope can give to a laity. Willmann went to United States in August 1977 for the Ninety-Fifty Annual Supreme Council Convention which took place from August 14 to 17 at Indianapolis in Indiana. Willmann led the Philippine delegation with Bro. Nicanor Y. Fuentes and Bro Concelio B. Cagurangan. Willmann later went to New York presumely to pay a visit to his sisters, Ruth, and Agnes Franciscan nun living in Roslyn, and his nephew James and niece Mary Ruth. The priest was prone to falls because of his weak limbs and had a fall while he was in New York, and needed a hip-bone surgery. The priest was initially confined at St. Francis Hospital in Roslyn. He was later transferred to the Murray-Weigel Hall, an infirmary probably owned by the Jesuits in New York state on September 8, 1977. Willmann was later discharged and stayed at the Jesuit House at Fordham. Willmann, died on September 14, 1977, due to cardiac arrest. Willmann's remains were interred at the Jesuit Cemetery in Novaliches, Quezon City, Philippines. The Knights of Columbus established its presence in the Philippines in early 1905, but Willmann was credited for cementing the organization's presence after he took leadership of the group after the World War II. The priest continuously resided in the Philippines since 1936. He also helped established the presence of various organization in the country such as the Daughters of Mary Immaculate (DMI) which was established as the Daughters of Isabella in 1951, Knights of Columbus Fraternal Association in the Philippines, Inc (KCFAPI), KC Foundations, Columbian Squires, and the Catholic Youth Organization (CYO).