At Aberdeen’s annual meeting earlier this month, Dons manager Derek McInnes said he was confident of bringing the player back to the Dons.
Hearts, Hibernian and MK Dons had all been linked with the attacking midfielder.
McGinn, who will officially become a Don again on Monday, joined the club in 2012 after leaving Celtic. He went on to make 222 appearances for the Reds, scoring 68 times, before leaving last summer.
He has been capped by his country 50 times.
Derek McInnes said: “Niall is a player I really enjoyed working with in the past so I was really keen to work with him again when the opportunity arose. I think he is a player who has always brought a high level of performance.
“Everyone from all the staff at the club, to his team mates, to the supporters, we will all welcome him back and we are looking forward to Niall picking up where he left off.”
Northern Ireland international Niall McGinn returns to Pittodrie
