Striker McClean pulled out of Nigel Worthington's Northern Ireland squad for Wednesday's night's "must win" Euro 2012 qualifier against the Faroes Islands amid speculation over a move from Derry to the north east.
And the 22-year-old has confirmed his plan to make himself available for the Republic despite playing at youth level for Northern Ireland.
"It was a blow seeing Irish League players being called up before me to the Northern Ireland squad, but having got the call I was relieved," McClean said in the Belfast Telegraph.
"However, it's always been my dream to play for the Republic and hopefully that will become a reality now that I'm going to be a Sunderland player."
McClean becomes the latest player to turn his back on Northern Ireland, taking advantage of a FIFA ruling that allows players from the island of Ireland to choose which national side they represent providing they have not played for the other in a competitive senior international.
Dan Devine, Darron Gibson, Shane Duffy, Marc Wilson, Daniel Kearns and Paul George have made the switch before him.
Although Worthington hopes to add Alex Bruce - twice capped by the Republic in friendlies - to the Northern Ireland ranks, the IFA have publicly bemoaned that the ruling has had a destabilising effect on them.
The IFA is today due to appoint 1982 World Cup hero Gerry Armstrong to the role of international player liaison officer, with one of his main tasks being to keep young players in the fold.
"Playing for Northern Ireland is a great honour - we need to make sure players realise that from a young age," Armstrong said in the Belfast Telegraph.
"I'm disappointed in James' decision but maybe this could be one of those scenarios where I intervene. Ultimately it will be Nigel's decision."