The 24-year-old winger has signed a two-year deal and becomes Dons boss Craig Brown's first summer signing.
The news comes almost a month after Aberdeen chief executive Duncan Fraser announced the signing of Hayes which the player then denied, leading to an embarrassing admission from Brown that Fraser had 'jumped the gun'.
The Irishman has spent the last three seasons at Inverness CT and has impressed, scoring 23 goals in the SPL from 85 appearances.
Hayes can play on the left side of midfield and the right, has also been capped three times at U21 level by the Republic of Ireland.
Brown told RedWeb: "I am just delighted he is joining us.
"Jonny Hayes will give us a new dimension, something that was lacking.
"We needed someone to go past people in a wide area and get crosses in. He is exactly what we are looking for."