He ran computer servers on the Darknet, enabling users to anonymously access millions of illegal images and videos showing children being raped and tortured.
Eric Eoin Marques, who is Irish and US citizens, has now been sentenced to 27 years in prison in the US.
In addition, the 36-year-old has to pay $ 87,000 in compensation to his victims.
The US judge in the case, Theodore Chuang, described Marques' acts as "despicable," as the "Independent" reports.
Prosecutor Ralph Paradiso said Marques created an online sexual predator community to anonymously abuse and exploit children and share the horrific images they created.
The public prosecutor's office had demanded that Marques be monitored for life after he had served his sentence.
The judge agreed, but allowed Marques to return to Ireland, where he last lived.
The US authorities had previously warned that no child in the world would be safe from Marques, no matter where they lived.
Marques pleaded guilty in February 2020 to having operated the server on the Darknet between 2008 and 2012.
The investigators found more than 8.5 million pictures and videos on the server, which also show violence against infants and young children.
Marques was living in Ireland at the time of the deeds and was extradited to the United States in March 2019.
kha / AP