Zenith National Insurance Corp. is a wholly-owned subsidiary of Fairfax. Based in Woodland Hills, California, Zenith is primarily engaged in the workers' compensation insurance business in the United States. Zenith conducts business in 46 states and the District of Columbia through independent agencies. In 2021, Zenith’s net premiums written were US$726 million. At year-end 2021, the company had statutory surplus of US$708 million and had approximately 1,400 employees.

Zenith operates through its subsidiaries Zenith Insurance Company and ZNAT Insurance Company. Zenith has been a specialist in workers’ compensation since 1951.

Zenith is led by its Chief Executive Officer, Ms. Kari Van Gundy.  Kari has been with Zenith for over 25 years and a part of Fairfax since the acquisition of Zenith in May 2010.