Tokio Marine will bring Pure Group under its umbrella within the financial year ending in March, the person told Reuters, asking not to be named because the information is not public yet.
Tokio Marine separately said its chief executive will hold a news conference in Tokyo at 4:30 p.m. (0730 GMT) regarding an overseas investment.
The Nikkei business daily reported the news earlier.
Japanese financial firms have been forced to look abroad for growth amid an ageing, shrinking population at home. Among its acquisitions, Tokio Marine bought Delphi Financial for $2.7 billion in 2011, after purchasing Philadelphia Consolidated for $4.7 billion in 2008.
With the purchase of Pure Group, Tokio Marine hopes to secure revenue in the market for insurance for high net worth individuals, the Nikkei said.