One will go into one inner ear and the other under her scalp from the single implant into her other ear - giving the 44-year-old woman much improved bilateral hearing.
Usually adults only have one implant fitted in one ear which leads to problems in noisy situations or finding where the sound is coming from.
A cochlear implant is an electronic device that can help both adults and children who have a severe to profound hearing loss.
It has two parts: an internal receiver/stimulator package and electrode array, and an external speech processor that looks like a hearing aid.
The device uses small electrical currents to directly stimulate the hearing nerve, which then sends signals to the brain where they are interpreted as sound.
The procedure has been developed at the South of England Cochlear Implant Centre (SOECIC), based at the University of Southampton.
Joint head of the centre Julie Brinton said: “Some adults and children have already received two implants, with one in each ear. The difference with the device being used today is that, although information is delivered to each ear, there is only one implant.”
Although around 40 of these devices have been implanted in patients in Europe, this is the first of its kind in the UK, the centre said.