Ibrahim Halawa, arrested at the age of 17 as part of a deadly crackdown on protests in Cairo, had faced the death penalty.
He flew into Dublin Airport on Tuesday to a welcoming party, having travelled on the plane with Sean O Regan, ambassador of Ireland to Egypt.
Writing on his Facebook page, he said: "Thank you so much to all the amazing people who made it today and to those who didnt i will be having a homecoming party for all :) thank you for everyone who made this happen :D much love to all."
Earlier, he posted a video of himself aboard the plane singing lyrics from Coming Home, a pop number by Skylar Grey.
Halawa is now 21 years old.
"Ibrahim has been through a hellish ordeal," said Maya Foa, director of Reprieve, a UK-based rights group that campaigns against the death penalty.
"Arrested and tortured, he faced a death sentence in a mass trial of 494 people for attending a protest when he was just 17. His release and return home to Ireland is long overdue."
Halawa's case highlighted human rights abuses carried out by the Egyptian government, Foa said.
"Ireland and the international community should call on Egypt to end these abuses," she said.
Arrested in August 2013 along with hundreds more, the tall, crop-haired student went on trial for an alleged role in violence during protests in Cairo - charges he, witnesses, and his lawyers, all denied.
During his time in jail, Halawa launched a hunger strike to protest his detention.
Egyptian officials repeatedly denied Halawa's health was ever at risk, but his family members and Irish politicians supporting his case claimed he was near suicide at one point.
|Halawa poses with his father Hussein Halawa as he arrives at Dublin Airport [Paul Faith/AFP/Getty Images]|
Source: Al Jazeera News