The late July High Court hearing will also involve Arch, Argenta and QBE.
Aon's Julie Page, Marsh's Chris Lay, former Home Secretary Amber Rudd, and ABI chair and Allianz UK chief Jon Dye join the initiative.
The executive switches to broking after working at Hiscox for nearly 12 years.
Property cat and D&F at 1 June, Aon pay cuts and industry pandemic response efforts