This study presents the retrofitting of the Church of the Transfiguration of the Lord in the Zagreb city center in the aftermath of the Zagreb and Petrinja 2020 earthquakes. Damage to this 1866 brick masonry building with compact floor plan, bell tower above the main entrance, tall walls, slender vaults and arches, dome above the sanctuary, and a roof with wood rafters included cracks in the masonry (walls, arches and vaults), and deformation of the upper portion of the bell tower. The retrofitting design was informed by a dynamic linear and non-linear numerical analysis in Tower 8 and 3muri software. Model with a stiffened bell tower and existing walls was on the border of satisfying the ultimate limit state for reduced seismic design load, but a new failure mechanism occurred with the transept wall failing on the opposite end of the church. Resulting design included strengthening of the masonry with the FRCM system, steel tie rods, RC tie beams and connecting it to the unified spatial steel structure within the attic and the bell tower. Additional RC arch was constructed in the attic wall opening beneath the bell tower, and narthex ceilings were reinforced by RC slabs. These retrofitting techniques were carefully and seamlessly merged with the existing architecture to preserve its original aesthetics while increasing the seismic resistance to LEVEL 3.