The mobile network will offer the red colour of the flagship Android handset from 4 August, joining the Amber Gold and Metal Grey models. Customers can get the new model on O2's Refresh tariffs with up to 8GB of data.
"Honed from a single piece of aluminium, the HTC One M8 continues to flaunt the attention to detail and innovation that earned the first generation HTC One (M7) a prestigious iF Design Award." said O2.
Aside from the colour, the device remains the same featuring a 5in Full HD screen, support for 4G LTE and the innovative Duo Camera with a depth sensor allowing users to refocus photos after they are taken.
O2's Refresh tariff means that customers only need to pay for monthly minutes, texts and data once they've had a phone for two years. Alternatively, they can upgrade early by simply paying what's left of that half of the contract.
The HTC One M8 is one of the best smartphones this year but it has strong competition from the LG G3 and Samsung Galaxy S5. Later this year the iPhone 6 is expected to arrive and will take on all these high-end Android devices.