The Department for Environment, Food and Rural Affairs (Defra) is migrating its 10,000 civil servants to energy-saving laptops.
The move is part of the department's ongoing Renew IT programme.
The move began last month and is set to be completed by the end of the year.
The cost of the move will be included in Defra's outsourcing contract with IBM.
The Renew IT programme will also reduce the number of pieces of hardware some employees operate, with the replacement laptops being used for remote and home working, instead of different Defra machines located in fixed locations.
The Lenovo ThinkPad laptops will be encrypted, and some will be accessed using fingerprint scans.