| Type: | bishop |
| Honorific Prefix: | The Most Reverend |
| Thaddeus Zielinski | |
| Prime Bishop of the Polish National Catholic Church | |
| Ordination: | November 3, 1927 |
| Consecration: | September 2, 1954 |
| Consecrated By: | Leon Grochowski |
| Birth Place: | Wilkes-Barre, Pennsylvania, United States |
| Honorific Suffix: | D.D. |
| Education: | Savonarola Theological Seminary |
| Elected: | 1967 |
| Term: | 19691978 |
| Death Date: | August 11, 1990 |
| Buried: | Holy Mother of the Rosary Cemetery. Cheektowaga, New York, United States |
| Predecessor: | Leon Grochowski |
| Successor: | Francis Rowinski |
Tadeusz "Thaddeus" F. Zielinski (191611 Aug 1990) was a bishop of the Polish National Catholic Church (PNCC). Zielinski was born in Wilkes-Barre, Pennsylvania in 1916 to Francis and Mary Kompinski Zielinski. He was consecrated in Buffalo, New York on September 2, 1954[1] and served as Prime Bishop of the Polish National Catholic Church from 1969[2] until his retirement in 1978.[3] Zielinski was the first American to serve as a bishop in the PNCC, and likewise, was the first bishop primate born in the United States. Zielinski died on August 11, 1990, at the age of 85 in Scranton, Pennsylvania.[4] During his tenure, the use of the English language, in place of Polish, was popularized with the translation of liturgies and hymns.[5]