At an event in London on Wednesday, EE said it would switch on its 5G service on 30 May, 2019.
“It is day one of our 5G journey,” said Marc Allera, CEO of BT’s consumer brands.
Vodafone had previously announced a launch date of 3 July.
The leap between current 4G technology and 5G is expected to be significant, with the next-generation network providing download speeds 50-times faster than its predecessor.
This would mean a typical HD movie would take just 13 seconds to download using 5G, compared to the average 10 minutes and 44 seconds it takes 4G.
EE said the new service will roll out to six UK cities to begin with: London, Birmingham, Manchester, Cardiff, Edinburgh and Belfast.
Other towns and cities around the country will then follow later in 2019 and 2020.
"We've started with 5G in some of the busiest parts of the UK, the widest range of 5G devices in the UK, and plans that give customers the best mobile connection and great benefits," Mr Allera said.
"We're adding 5G to the UK's number one 4G network to increase reliability, increase speeds, and keep our customers connected where they need it most. 5G will create new experiences with augmented reality, make our customers' lives easier, and help launch entirely new businesses that we haven't even imagined. We're upgrading more than 100 sites to 5G every month from today to connect more places to what 5G can enable."