Network Rail already manages the entire St Pancras International station, and the domestic station is the company’s 18th major station across the country.
The £70 million cost includes the civils and construction work delivered by Union Railways North (URN) and Network Rail’s signalling, telecoms, and systems work.
First Capital Connect invested an additional £1.2million for the general fit out of the station including items such as gatelines, internal staff accommodation and ticket machines.
The improvements will also enable passengers from outer London stations such as St Albans, Luton, Croydon and Brighton to connect directly with Eurostar services to Europe, and to the wider rail and London Underground network, cutting precious minutes off journey times.
Ms Kelly, said: “This new station will improve the daily journey to work for thousands of passengers, providing extra capacity and better transport links. It means we can tackle overcrowding and deliver longer trains under the £5.5bn Thameslink modernisation scheme.”
The government is also spending £1bn to improve the tube and mainline stations at King's Cross.
Iain Coucher, Network Rail's chief executive said: “The opening of our new station is the latest piece of the jigsaw in transforming one of London’s most prestigious stations.”