Roman Maria Jakub Próchniewski (February 29, 1872 in Congress Poland - February 13, 1954 in Płock, Poland) was the Prime Bishop of the Mariavite Old Catholic Church from 1945 to 1953.

[1] He graduated from the Saint Petersburg Roman Catholic Theological Academy.

[2] He was a confessor of Maria Franciszka Kozłowska, the founder of the Mariavite movement, and the author of theological and Mariavite-themed articles.

He wrote a book about Maria Franciszka Kozłowska titled Żywot Przeczystej Pani i objawione jej Dzieło Wielkiego Miłosierdzia (Life of the Pure Lady and her Revealed Work of Great Mercy).

He was the main consecrator of Bishop Zygmunt Szypold who became the head of the Polish Old Catholic Church.