The account, which is believed to be worth a substantial six figures, was handed to Biss Lancaster following a four-way pitch. Citigate previously held the account for ten years.
The news comes days after the firm announced sweeping restructures to the business in a bid to tackle expected $7.1bn losses in the year to March.
Biss Lancaster will be responsible for CSR, product support and issues management.
It will be handling comms around last month's annoucement that a consortium including Hitachi has been awarded a £7.5bn contract from the Department of Transport to build and maintain a new fleet of high speed trains in the UK.
European director Andrew Robinson will lead the account, reporting into Hitachi Europe's PR manager Daniela Karthaus. Robinson said: 'From high speed trains to finger vein scanning, there is a wide range of products, services and issues to manage'.