Casimir Grotnik was born in 1935 in Jeziorzany, Poland, to Franciszek and Apolonia Jablonski Grotnik. He was ordained a priest on April 20, 1958, by the bishop of Lublin, Piotr Kalawa. Grotnik immigrated to the United States in 1969 and served as a priest in the Central Diocese of the Polish National Catholic Church. In 1996, Grotnik received a doctorate in Old Catholic historical theology at the Christina Theological Academy in Warsaw, Poland. He was consecrated a bishop in November 1999. From that point, he served as the bishop ordinary of the Central Diocese and the pastor of St. Stanislaus Polish National Catholic Cathedral in Scranton, Pennsylvania, until his death on December 9, 2005.