He currently serves as an auxiliary bishop of the Diocese of Brooklyn. Mroziewski was born in Augustów, Poland. He went to the Catholic university in Lublin, Poland where he earned his masters in theology in 1991.
He was ordained a priest by Bishop Juliusz Paetz on June 29, 1991.
Mroziewski was appointed Titular Bishop of Walla Walla and Auxiliary Bishop of Brooklyn on May 19, 2015 by Pope Francis. He received his episcopal consecration on July 20, 2015.