Ibrahim Halawa has been acquitted of all charges in Egypt after four years in jail.
Due to procedures within the Egyptian judicial and prison authorities, it is unlikely the Irishman will be released immediately, however.
Mr Halawa (21) had been charged over Muslim Brotherhood protests which took place in Cairo in August 2013.
The student and son of a prominent Muslim cleric in Dublin, Sheikh Hussein Halawa, was jailed after being detained in a mosque near Ramses Square in Cairo four years ago amid protests over the removal of president Mohamed Morsi.
He was 17 at the time.
Along with scores of others he was accused of murders, bombing, possession of firearms and explosives, arson, violence against police and desecration of Al Fatah Mosque.
He was cleared of all charges on Monday.
Taoiseach Leo Varadkar welcomed today's news.
“I have just received news from our Embassy in Cairo that the Egyptian courts have delivered an acquittal in the case of Irish citizen Ibrahim Halawa, and that Ibrahim’s sisters Somaia, Fatima and Omaima have similarly been acquitted," he said.
“I wholeheartedly welcome this conclusion to what has been an extraordinarily protracted case.
“Now that Ibrahim has been cleared of all charges, I expect he will be released as soon as possible and can return home to his family. The Government will facilitate his return home at the earliest opportunity.
“I want to acknowledge the consular and diplomatic work undertaken on Ibrahim’s behalf by the Department of Foreign Affairs and Trade and the Irish Embassy in Cairo throughout this lengthy process. Following today’s verdict, they will continue to assist Ibrahim and his family to ensure he gets home as soon as possible.”
President Michael D Higgins 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.
"I am sure Ibrahim’s family are looking forward to the moment that Ibrahim will return to his home and loved ones.”
Foreign Affairs Minister Simon Coveney also welcomed Mr Halawa's acquittal.
"On behalf of the Government and on my own behalf I welcome the news from Cairo that Ibrahim Halawa has been acquitted.
"This is the good news we had been hoping for.
"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," said Mr Coveney.
He added: "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.
"We are conscious that there will be some practical procedures and formalities to be gone through before Ibrahim will be able to fly back to Dublin, but my Department and our Embassy team will be assisting and supporting Ibrahim and his family to seek to ensure he gets home as soon as possible."
Ireland's Children's Minister Katherine Zappone said Mr Halawa's acquittal must be followed by a swift return home.
"It is important that all who campaigned over the past four years continue to co-operate to ensure Ibrahim's return is arranged as soon as possible.
"I remain in close contact with Ibrahim's sister Somaia, his lawyers and Government colleagues to ensure that Ibrahim's needs are immediately assessed and any supports required put in place.
"Assessing his health, psychological and social needs must be the priority and supports offered," she said.
Sinn Féin leader Gerry Adams said: "I welcome the news that Ibrahim Halawa has been acquitted.
"It is now imperative that the Egyptian government guarantees his safe return to Ireland as soon as possible.
"Ibrahim has spent four years in a jail far from his home and family. His incarceration represents a violation of his basic human rights. His physical and mental health suffered greatly as result of his imprisonment. His treatment by the Egyptian authorities was an affront to human decency."