Virgin Trains say half of all their West Coast services will be worked by their new Pendolino tilting trains by the end of March.
The fleet of 53 trains is costing Virgin £1bn to run and maintain
More than 500 services a week will be served by the trains - 50% of the West Coast Mainline train service.
The £11m trains are able to tilt around curves and run at 125 mph.
From September, Virgin are promising the fastest journey between London and Birmingham, taking just one hour and 23 minutes.
Chris Green, Virgin Trains chief executive, said: "This is a real milestone in the transformation of the West Coast.
"Most of our passengers are already experiencing Pendolino travel and many thousands will be able to do so from the end of this month."
As the new trains are brought into service older trains will be withdrawn.
The fleet of 53 Pendolino trains is costing Virgin £1bn and so far 100 miles of the West Coast Mainline has been upgraded by Network Rail.