Mitsui Sumitomo Acquires 15.7% Stake in U.S. Insurer, Joins Board

Mitsui Sumitomo Insurance Co. of Japan disclosed in a Schedule 13D amendment filed March 5 that it has raised its stake in W. R. Berkley Corporation (NYSE: WRB) common stock to 15.7% through open-market purchases and has nominated its executive Andrew Carrier to Berkley’s board. Under a Rule 10b5-1 trading plan, Mitsui Sumitomo acquired roughly 2.32 million shares between February 9 and March 3, including about 560,000 shares bought over February 17–18 at a cost of approximately $40 million (around 500 billion KRW), bringing its total holdings to 58,780,450 shares. In the amendment, parent company MS&AD Insurance Group denied any beneficial ownership exceeding mere economic interest or a “joint holder” status, yet confirmed that it entered into a new LLC agreement with Family Holdings (which holds Berkley family shares) and exercised board-entry rights under an existing framework agreement.

Berkley had already announced in December 2025 that Mitsui Sumitomo held at least a 12.5% stake, underscoring the insurer’s role as a long-term strategic shareholder. MS&AD likewise cited acquiring up to 15% of Berkley shares as a cornerstone of its plan to invest up to $5 billion (approximately KRW 6–7 trillion) to double North American property & casualty insurance profits.

W. R. Berkley, headquartered in Greenwich, Connecticut, is a property & casualty and reinsurance holding company operating across the U.S., Europe and Asia, with a focus on specialty commercial insurance and reinsurance and the majority of its revenue derived from P&C underwriting. MS&AD Insurance Group, one of Japan’s largest property & casualty insurers—comprising Mitsui Sumitomo Insurance, Aioi Nissay Dowa and others—is bolstering its overseas expansion, including equity investments in North American insurers and asset managers, to offset the low-growth domestic market.