He became a close friend of the painter Angelica Kauffman, whose cousin Rosa Florini he married in 1775. The next year he produced a design for a proposed sacristy for St Peter's in Rome, which may indicate that he visited his native city at around this time. In 1783 Kauffman persuaded Bonomi to move back to Rome, where she was now living. He took his wife and children with him, and the move seems to have been intended to be permanent; however the next year the family returned to London, where Bonomi was to remain based for the rest of his life.