 Koudelka was ordained to the Roman Catholic priesthood November 29, 1875, for the Diocese of Cleveland by Tobias Mullen, bishop of Erie, Pennsylvania.On November 29, 1907, Pope Pius X appointed him auxiliary bishop of the Diocese of Cleveland and he was ordained on February 25, 1908 with a special ministry to the Slavic community.On June 24, 1911 Pope Pius X appointed him auxiliary bishop of the Archdiocese of Milwaukee.