Who completed the dome of St. Peter's Basilica after Michelangelo's death?

Giacomo della Porta completed the dome of St. Peter’s Basilica after Michelangelo’s death.

Michelangelo redesigned the dome in 1547 and supervised its progress until his death in 1564, when the drum was complete but the dome itself remained unfinished. His plans and wooden model provided the essential design for the final construction.

In 1585, Pope Sixtus V appointed Giacomo della Porta to resume the work, with Domenico Fontana assisting. They modified aspects of Michelangelo’s design, including the profile and structural proportions, and completed the dome to the base of the lantern in 1590. Fontana later finished the lantern, whose orb and cross were raised in 1592.

Bramante and Raphael were earlier architects involved with St. Peter’s overall project, not the people who completed Michelangelo’s dome. Michelangelo therefore remains its principal designer, while della Porta is credited with bringing it to completion.