Nokia already supplies the UK telecoms group with 3G equipment and will now replace Huawei in the group’s 2G, 4G and new 5G systems as well.
Huawei has been accused of being a security risk with allegations its equipment can be accessed by the Chinese government.
In July, the UK banned all mobile providers from using the firm’s kit starting at the end of the year.
All Huawei equipment must also be removed from UK 5G networks by 2027.
BT's EE arm currently uses Nokia equipment in areas of London and the Midlands, but this will be now extended to other cities such as Exeter, Southampton, Cambridge and Dundee.
"With this next stage of our successful relationship with Nokia, we will continue to lead the rollout of fixed and mobile networks to deliver stand-out experiences for customers," BT's chief executive Philip Jansen said in a statement.
The UK telecoms giant is expected to use another supplier to provide 5G kit to avoid being over-reliant on Nokia.
BT has already used Ericsson as a replacement for Huawei in the systems at the heart of its networks and commentators expects it to be used as the second supplier of masts and antennae as well.
BT shares dipped to 99.7p.