Michael McMonagle (42), from Limewood Street in Derry, changed his plea when he appeared at Derry Crown Court on Monday after previously denying the charges.
The former journalist had originally faced 15 charges, including attempting to incite two children to engage in sexual activity.
He was also accused of 13 counts of attempted sexual communication with a child.
The offences took place on dates between May 2020 and August 2021.
At his first court appearance in 2023 he was charged with three offences before 12 more offences were added later to the bill of indictment.
He confirmed his name, his address and date of birth when he was re-arraigned at Derry Crown Court today, .
When the charges were put to him by the court clerk, he pleaded guilty to 14 of the 15 offences.
A prosecution barrister said another charge was being left on the books and would not be proceeded without the leave of the Crown Court or the Court of Appeal.
The court was told that a pre-sentence report would be prepared by the Probation Board and a psychological assessment would be carried out.
McMonagle was also placed on the sexual offenders’ register. How long he will be on the register will depend on the length of the sentence imposed.
Before releasing him on bail, Recorder of Derry Judge Neil Rafferty KC said it was likely a prison sentence would follow.
The case was adjourned when a plea and sentenced hearing will take place Friday, November 8.
McMonagle worked for a time as a journalist in Derry before switching to become a Sinn Féin press officer in the city.
He was also a party adviser at Stormont.
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