A new rail link from the north-east of England to London is due to carry its first fare-paying passengers.
Trial runs with the new engines have proved successful
Grand Central's Sunderland to King's Cross service has been dogged by delays and was due have started last year.
Problems with the delivery and refurbishment of rolling stock prevented the East Coast Main Line service launching as planned.
But the firm said it was now able to offer a limited service, with the first train departing at 0646 GMT on Tuesday.
'Checks and upgrades'
Grand Central will run one return service per day, with stops in Teesside and North Yorkshire, until 23 December. It plans to restart services again on 27 December, after a programme of track maintenance.
Managing Director Ian Yeowart said: "We expect to have the full timetable up and running by the middle of January, when all the rolling stock has gone through the necessary maintenance checks and upgrades.
"It is very important for the crews to start before Christmas, they have been with us for about 11 months and they are chomping at the bit to get started."
Mr Yeowart said passengers would initially be able to buy tickets on the train until its web-based ticket purchasing system was up and running.
The company is selling single journey tickets for £44 and £69 for return trips. First class fares are double.
The new service will call at Hartlepool, Eaglescliffe, Northallerton, Thirsk and York.