The deal will be completed through Butterfield’s wholly owned subsidiary, Butterfield Bank (Guernsey).
ABN Amro Channel Islands offers banking, investment management and custody services to private clients, trusts, and funds in Jersey and Guernsey.
It had £2.9bn in deposits and £3.5bn in assets under management and custody at the 31 December 2018.
The deal is expected to close during the third quarter of 2019, subject to regulatory and other customary closing conditions.
After closing the deal, ABN Amro’s Channel Islands business and employees will be integrated with the existing Butterfield Guernsey operations and operate under the Butterfield name.
The acquisition of ABN Amro Channel Islands will allow the Bermuda-based firm to expand its presence in Jersey and Guernsey.
Michael Collins, Butterfield’s chairman and chief executive, said: “In ABN Amro Channel Islands, we have found an ideal partner through which to expand our core Channel Islands banking business.
“This acquisition is another important step in our strategy to grow through acquisitions in the highest quality offshore markets where we have scale and expertise.
“It underscores our continuing commitment to expand Butterfield’s presence in the Channel Islands and the importance of these two jurisdictions to our multinational clients.
“ABN Amro Channel Islands brings a conservative risk management culture, similar to that of Butterfield, and will contribute both management talent and sales expertise to our combined business.
“This represents an excellent opportunity for clients and employees, and we look forward to welcoming our new colleagues to Butterfield.
“Together, we bring long histories of client service at the highest level.”