The fan, Andrew Duffy, 24, from Termon, is believed to have drowned in the Canal at Binn’s Bridge at Phibsboro.
The well-known Termon GAA player had been at the game earlier
His body was taken from the Canal after midnight and he was pronounced dead just before 1am.
Gardai have described the incident as a tragic accident.
It is understood that he had been making his way back to where he was staying when he slipped and fell into the water.
A full investigation has been launched into the circumstances surrounding the death.
Former TD and local GP Jim McDaid said his nephew was with Andrew when the accident happened.
“It is heartbreaking for the entire family and people around Termon and beyond,” said Dr McDaid.
“The family are lovely people and for this to happen on a day when Donegal was celebrating such a brilliant victory is just so tragic.”
Andrew’s home parish of Termon was in mourning at the death of the young man.
He played senior football for Termon GAA team and was hugely respected in the community.
He had been part of a talented young side which had won the All-Ireland Gaeltacht Junior championship.
His father John, a Waterworks Caretaker with Donegal County , mother Margaret and sisters Leanne and Caroline were last night being comforted by family and friends.
A special mass in his memory was attended by hundreds of people including members of the Donegal Senior Football team at St Columba’s Church in Termon tonight.
Chairman of the Termon GAA club, Joe McDaid, said Andrew was a modest and quiet young man whose death had numbed the community.
“Andrew was such a lovely young fella and was quiet and modest. He farmed and did a lot of fencing.
“People are waking up to hear this news and they just can’t believe it has happened.
“It has taken the whole shine off Donegal’s win for us. People are thinking about getting tickets for the All Ireland final but we’re just thinking of poor Andrew and his family.
“It’s just awful what has happened,” he said.
In a statement this evening Termon GAA club said: “Termon GAA was rocked to its core this Monday morning with the news of the tragic death of club member and senior team member Andrew Duffy. The club would like to offer its condolences to Andrew’s family at this heart-breaking time. Our thought and prayers are with them.
“Andrew represented the club at all age groups and was part of a very successful minor team which won county honours, but it was at senior level that Andrew excelled. Andrew won reserve player of the year in 2010 and made the breakthrough to being a regular starter for our senior team this season. Indeed, Andrew was the holder of his own All Ireland medal having played a significant role in Termon winning the All Ireland Junior Gaeltacht title earlier this year. While scant consolation now, the last game of Gaelic football which Andrew saw between Donegal and Cork was one in which so many of the characteristics he himself brought to the game were on show: courage, skill, honesty and work rate were all evident in Croke Park and were always on display when Andrew wore the club colours.
“If you had to pick one person to embody all the positive things in Termon GAA club, Andrew Duffy would have been that person. You will be sorely missed Andrew. Ar dheis de go raibh a anam.”