Signorelli, who is currently group chief underwriting officer, will succeed James Shea, who has decided to leave Zurich to pursue opportunities outside the company.
Signorelli joined Zurich in July 2017 and has held senior leadership positions in the United States, Asia and Switzerland.
She “successfully transformed” the underwriting function, strengthened its resilience, and ensured delivery of differentiated services and solutions to customers.
Mario Greco, group CEO, said: “Sierra has extensive experience and knowledge of the insurance industry and is a proven and passionate people leader. Her broad skill set, her deep understanding of our business and culture, and her strong customer focus make Sierra the perfect fit for this role.