A court in Egypt has acquitted Ibrahim Halawa of all charges.
The verdict was announced at a court near Cairo this afternoon.
The Irish Government has said they are working to get him home 'as soon as possible', and expect him to be released from custody 'without delay'.
A verdict had been expected at the end of August, but the hearing was adjourned until today.
Mr Halawa (21), from Firhouse in Dublin, has been held in an Egyptian jail since his arrest during demonstrations against the ousting of president Mohammed Morsi in August 2013.
Ibrahim Halawa, moments after his acquittal. He jumped with joy, hugged fellow prisoners and had tears in his eyes. pic.twitter.com/P40IjYQLHK
— Declan Walsh (@declanwalsh) September 18, 2017
His mass trial - alongside hundreds of other defendants - was adjourned more than two dozen times.
Ibrahim's sister Fatima says they screamed with they heard the news this lunchtime.
"We're overwhelmed, we're excited [...] We're finally glad it's all coming to an end," she said.
Groups such as Amnesty International and a number of Irish politicians have campaigned for Mr Halawa's release.
Amnesty's Colm O'Gorman announced the news of the acquittal on Twitter:
Breaking: Ibrahim Halawa has been acquitted of charges. Verdict just emerging in Cairo. Really, really good news. #FreeIbrahim
— Colm O'Gorman (@Colmogorman) September 18, 2017
In a statement, Mr O'Gorman welcomed the outcome, saying "not one shred of evidence" was presented against Ibrahim over the course of the trial.
However, he added: “While Ibrahim’s release puts an end to the gross injustice in his case, it is utterly disgraceful that the Egyptian authorities continue to hand out heavy sentences to other protesters after sham mass trials that flout the most basic standards of a fair trial, while security forces who used excessive and lethal force killing at least 97 protesters that day have escaped unpunished."
Foreign Affairs Minister Simon Coveney has welcomed this afternoon's news.
He said in a statement: "Ibrahim Halawa’s name has been cleared and his innocence is confirmed. I look forward to him being released from custody without delay.
"My thoughts are with Ibrahim and his family at this time of great emotion for them.
"The Government’s priority now is to support Ibrahim and his family in every way that we can in order to ensure that Ibrahim is able to return home to his family and friends as soon as possible."
Minister Coveney added that some 'practical procedures and formalities' will have to be gone through before the Dublin man can fly back to Ireland.
Taoiseach Leo Varadkar said he "wholeheartedly welcomes" the conclusion to an "extraordinarily protracted case".
President Michael D Higgins, meanwhile, said: “As President of Ireland I welcome the news that Ibrahim Halawa and his three sisters have today been acquitted of all charges brought against him, and them, in what has been a prolonged, distressing and draining experience.
"Today’s decision brings to an end a long ordeal that Ibrahim, his family, friends and legal team have been put through."
Both the Taoiseach and President Higgins acknowledged the efforts of the Department of Foreign Affairs and Trade and the staff at Ireland’s embassy in Cairo during the 'lengthy process'.