Passengers travelling from England to France through the Channel Tunnel will be able to connect to Vodafone and EE mobile phone networks for the first time from March.
EE - which includes Orange and T-Mobile - and Vodafone will initially offer 3G services but will bring 4G in the future.
Customers travelling from France to England have been able to access 3G services since 2012, when Orange introduced mobile connectivity beneath the sea just before the London Olympics.
A new 10-year contract will now mean that passengers using the north tunnel, through which the car-carrying shuttle and the Eurostar travels, will be able to make calls, check emails and surf the internet from 100 metres below sea level.
"Being connected is such an important part of travelling now and this will be another route we've covered with 4G, making a huge difference to millions of customers who can now make the most of their journey time," said Fotis Karonis, Chief Technology Officer at EE.
British networks O2 and Three are reportedly in talks with Eurotunnel to bring the service to their customers in the future. Until then, customers will be able to benefit from the EE and Vodafone networks by manually switching to their services, however doing so would incur additional costs.
John Keefe, a spokesperson for Eurotunnel, said: "We are talking with the other operators to see whether they would like to join in as well. There is capacity for all the operators to use the equipment that is down there at the moment."