Train services from West Norfolk to London will become half-hourly with the arrival of a new franchise later this year.
Govia Thameslink will be taking over the service currently operated by First Capital Connect.
Passengers will also be travelling in new carriages which are being rolled out across the line providing 50 per cent additional capacity.
Some 1,140 new carriages are already under construction and new tunnels will be built to link Peterborough and Cambridge.
Govia has also pledged to improve stations and offer free wifi at more than 100 of them.
Staffing will also be increased at 100 of the largest stations to ensure there will be personnel from the first to last trains.
“A world class railway is a vital part of our long-term economic plan. New state-of-the-art trains, more seats, better connections and improved stations will transform travel across London and the south east,” said rail minister Stephen Hammond.
Managing director at First Capital Connect, David Staltham, said the company was disappointed that it had not been selected as the franchise operator.
“I am tremendously proud of the improvements we have brought to the FCC franchise, and our role as a key partner in the Thameslink Programme.
“Everyone at FCC is committed to continue operating to the highest standards until the new franchise begins,” he added.
The Govia franchise will last for seven years and will include routes from Brighton, Gatwick Airport, Luton, Bedford, Peterborough and Moorgate, as well as the line from Lynn to London King’s Cross.
Govia will take over the existing Thameslink and Great Northern franchise (operated by FCC) from September 14 this year.
It will also include the South Central franchise (Southern and Gatwick Express) from July 26 next year.
Half-hourly trains from Lynn to London have been pledged once an upgrade is carried out at the Ely North junction.
The new operator will also develop website, smartphone and tablet apps to make door-to-door travel easier for passengers, including buying tickets and booking taxis.