UK rail and bus operator FirstGroup has been awarded the newly-created Greater Western and Thameslink-Great Northern rail franchises.
FirstGroup operates rail and freight train services across the UK
The firm said the franchises were worth more than £1bn in revenues a year.
FirstGroup added that the award meant it was now the UK's largest rail operator, carrying more than 260 million passengers per year.
The firm will pay the government £1.81bn for the two franchises, which both begin on 1 April 2006.
Rival rail operators National Express and Stagecoach were also bidding for both of the franchises.
FirstGroup currently operates a number of passenger and freight rail services in the UK, although some of its passenger routes are being absorbed into the new franchises.
The 10-year contract for Greater Western combines the existing First Great Western and Link franchises, both of which FirstGroup already runs, and Wessex services currently operated by National Express group.
The Department for Transport said the Greater Western franchise committed FirstGroup to operate services from London to the South West and South Wales.
As part of the deal FirstGroup must also retain the overnight sleeper between London and Penzance, and keep the half-hourly off peak service between London and Cardiff.
Five firms had been bidding for the new Thameslink-Great Northern franchise, which begins in April 2006 for nine years.
The new route will operate passenger services mainly to the north of London, including the current Thameslink routes.
FirstGroup will run services from Brighton, through London and on to Bedford, and from London to Cambridge, Kings Lynn and Peterborough.
FIRSTGROUP'S CURRENT RAIL SERVICES
First Great Western
"We are delighted to be awarded both of these franchises and look forward to delivering the improved performance, capacity, facilities and customer benefits proposed in our winning bids," said Moir Lockhead, group chief executive.
Transport secretary Alistair Darling said: "The contracts have been awarded following a rigorous, competitive and independent bidding process.
"Both are tough and will deliver value for money for the taxpayer and an improved service for passengers."