The will bring additional capacity to services along the West Coast Main Line and in North Wales.
The new, state of the art trains will start operating in 2022 and will be a mix of 10 seven-carriage electric trains and 13 five-carriage bi-mode trains, with the ability to switch seamlessly between electric and diesel power.
The electric trains will operate between London, the West Midlands and Liverpool while the bi-mode version will serve the London to North Wales route.
They are fast-accelerating 125mph trains which draw from their Japanese bullet train heritage. As a result of their modern design, passengers will enjoy a quieter journey compared to the diesel-only trains they will replace.
The new trains will have better and more reliable free Wi-Fi, at-seat wireless inductive charging for electronic devices, plug sockets and USB slots; a brand-new catering offer and a real-time passenger information system that can advise customers of connecting rail services.
There are 453 seats on a seven-car service and 301 seats on a five-car service increasing compacity compared to the Class 221 Voyager trains they replace - which have 258 seats.
The seven-carriage version of the electric trains will have similar numbers of seats to a nine-carriage Pendolino, owing to the longer 26-metre carriages of the Hitachi trains.
The new trains will be built at Hitachi’s factory at Newton Aycliffe in north-east England, supporting thousands of jobs across the country.
Steve Montgomery, managing director of First Rail, said: "We look forward to beginning our Avanti West Coast services on Sunday 8 December, and these new trains will help us really improve travel for passengers with more services, more seats, a better journey experience, enhanced catering and added comfort."
Ernesto Sicilia, Trenitalia UK managing director, said: "We are pleased to announce this new fleet which highlights our commitment to innovation and desire to constantly improve our services. We are delighted to provide more efficient and modern trains which are sustainable and environmentally friendly, reducing CO2 emissions by 61 per cent, including new comfortable seats for an improved customer experience."
The investment in these new trains is being financed through Rock Rail West Coast, a joint venture between Rock Rail and Aberdeen Standard Investments. Rock Rail West Coast will own the trains and lease them to First Trenitalia.
The contract also includes an agreement for aspects of the 23 new trains to be maintained by Hitachi Rail. First Trenitalia have also signed a maintenance agreement with Alstom enabling the fleet to be maintained by a joint team from Hitachi and Alstom at the existing Oxley depot in Wolverhampton, supporting highly-skilled engineering jobs.