Mobile operator EE will charge new UK customers extra to use their mobile phones in Europe from January.
Those joining or upgrading from 7 July 2021 will be charged £2 a day to use their allowances in 47 European destinations from January 2022.
EE, which is part of BT Group, previously said it had no plans to reintroduce roaming charges in Europe.
It is the first UK operator to reintroduce the charges since the EU trade deal was signed in December.
Since 2017, mobile networks in EU countries have not been allowed to charge customers extra to use their phones in other EU countries.
There are some "fair use" limits, for example, you cannot get a mobile phone contract from Romania and then use it all year round in Italy.
In January 2021, EE, O2, Three and Vodafone all stated they had no plans to reintroduce roaming charges, despite Brexit giving them the option to do so.
EE said on Thursday that introducing the charges would "support investment into our UK based customer service and leading UK network".
However, it will not charge UK customers extra to use their phones in the Republic of Ireland.
Customers travelling to the 47 affected countries will be able to buy 30-day passes to use their home tariff abroad. The cost of those will depend on which tariff customers are on.
On Wednesday, it was reported that O2 was going to reintroduce roaming charges.
However, it is merely adding a "fair use" data cap of 25GB a month and will not charge customers more to use their phones in the EU.
Fair use limits are normal and were allowed when the UK was still part of the EU. From next month, Three will be reducing its fair use limit from 20GB a month to 12GB.
The UK's trade deal with the EU says that both sides will encourage operators to have "transparent and reasonable rates" for roaming, but it did not ban charges.
The government's guidelines encouraged people traveling in Europe to check with their mobile operators to find out about any roaming charges.