The merged entity will have a Nasdaq listing and an opening market value of around $550mn.
CFO John Parry, who joined the firm last year after holding the same role at Lloyd’s, will become interim CEO.
Dr Bernard Bailey and Fred Donner will stand for election at the Argo annual shareholders meeting on 16 April.
The surprise move reflects a desire to bolster profitability at the specialty business, group CEO Buberl says.