Thomas McKenna, a former Gaelic Athletic Association (GAA) official in Co Armagh, has admitted to a "catalog of terrible offenses" against more than 20 vulnerable young men.
McKenna, 62, a former treasurer with Armagh GAA club Crossmaglen Rangers, had been due to go on trial to face almost 150 charges, including several rape, serious sexual assault, and indecent assault offenses.
Many of the charges involved offenses against children.
The offenses were said to take place over the course of almost 30 years between December 1989 and August 2018, when McKenna was arrested.
McKenna appeared at Belfast Laganside Court on Thursday morning to be re-arraigned with the charges he faced. RTÉ News reports that it took almost 30 minutes for the charges to be put to him.
McKenna pleaded guilty to all charges put to him.
Judge Patricia Smyth told McKenna that he would be "punished severely" when he returned for sentencing later in the year.
She also spoke directly to some of McKenna's victims, who were watching the trial via video link, praising them for their courage in coming forward.
"I praise your courage in coming forward to disclose these terrible crimes in very, very difficult circumstances," Judge Smyth said.
"Today each of you is completely vindicated in the complaints you made against this man and I hope that vindication will bring you some peace of mind to those of you who still suffer grievously.
"Each of you has done a great public service in coming forward and I want to thank you for that."
McKenna pleaded guilty to 23 offenses in June last year, including 18 counts of voyeurism, four counts of indecent assault, and one of making an indecent picture of a child.
At a previous hearing, the court heard that McKenna took pictures and videos of his victims without their permission, while police told a hearing that they retrieved 43,000 images and 8,000 video clips from devices they seized.
McKenna had previously denied 148 offenses which were put to him on Thursday morning.