It intends to launch the next-generation service in Belfast, Cardiff, Edinburgh, London, Slough and Leeds and then expand to a total of 50 towns and cities by summer 2020.
It will be the last of the UK’s network coverage providers to roll out 5G.
However, it will be the only one to do so without using equipment from the embattled Chinese telecoms equipment-maker Huawei.
O2 is owned by Spain’s Telefonica, which has used Huawei’s infrastructure in some of its other networks.
Moreover, O2 trialled some of Huawei’s 5G radio access network gear at cell towers in the UK before deciding to opt for rival products from two vendors it had already used to deliver 4G.