Sheola Keaney was found strangled in a laneway in Cobh two days after she went missing earlier this year.
Thomas Kennedy from Russell Heights in Cobh is due to be sentenced tomorrow.
Ms Keaney went missing on 14 July and a search took place for her in Cobh involving gardaí, her family and friends. She had been socialising and was last seen in the company of Mr Kennedy in the early hours of the morning.
The couple had split up two months previously after an 18-month relationship.
Mr Kennedy had given gardaí conflicting accounts of Sheola Keaney's final hours. He first said that she had stayed at his house and slept in his sister's room before leaving at 10am the following morning.
However after his arrest, Mr Kennedy said they left the house together mid-morning and walked to the laneway at Newtown where her body was found two days later.
He said he had caught Ms Keaney from behind and put his left arm around her neck and only let go when both fell to the ground.
He then wrapped Sheola's body in two refuse sacks, dumped it in the laneway and covered it with metal bars and hedge cuttings.
When Thomas Kennedy was arraigned last Tuesday he had pleaded not guilty to murder. 150 witnesses were listed for the trial which was expected to last until Christmas.
However, he was re-arraigned at his own request just before lunch this afternoon and pleaded guilty to Sheola Keaney's murder. No explanation was offered for the change of plea.
Mr Justice Paul Carney will hear an outline of the case from gardaí as well as victim impact statements from the Keaney family before passing sentence on Thomas Kennedy tomorrow.
