Other areas of the UK will begin to receive coverage in 2020 to coincide with the wider availability of 5G phones, O2 said.
The technology is regarded as the “next generation” of mobile communications, expected to offer internet speeds several times faster than 4G as well as being able to support more devices on a network at once and greatly reduce lag or delay in connections.
Fellow operators EE and Vodafone are already running trials of 5G networks in parts of the UK.
Mark Evans, chief executive of O2 parent company Telefonica UK, said: “5G is a promise of so much more – for consumers, business, industry and public services.
“O2 is working in partnership with British industry, encouraging businesses, big and small, to engage with the possibilities of 5G technology through both our testbed programme and launch deployment.
“O2’s 5G network will arrive this year and we want the next generation of mobile services to launch with a bang. 5G will benefit customers from launch, with better speeds and improved customer experience.”
O2 said its rollout would also include the creation of new “5G innovation spaces” across the country aimed at businesses that the firm says will “help fuel future innovation that will boost the British economy post-Brexit”.
“Following the demand from our FTSE 100 trials, we are extending our testbed opportunities so that businesses of all sizes can work with us to build the 5G economy,” Mr Evans said.
“Mobile is one of the UK’s most powerful opportunities to strengthen our economy and improve the lives of British people and 5G is a significant milestone for this nation.”