The 28-year-old has put pen to paper on a three-year deal and will join Aberdeen in the summer.
In the meantime he’ll see out the season with Inverness as he looks to help the Highland club avoid relegation from the Ladbrokes Premiership.
Tansey was the subject of a transfer bid from Aberdeen in the 2016 January transfer window. Despite reports of the Dons triggering a release clause, the deal wasn’t completed in time before the window closed and Tansey remained in the Highlands.
Speaking to the club’s official website, Aberdeen boss Derek McInnes hailed the signing.
He said: “He is a player we have admired for a long time and he will be a very welcome addition to the squad here at Pittodrie.
“He is a confident player, exactly the type of player we want to see at our club. There is more to come from Greg and I’m sure we will provide the perfect platform for him to develop.”
Tansey has enjoyed two spells with Caley Thistle. Originally signing in 2011, he joined Stevenage a year later before returning in January 2014. He was a member of the Inverness side that won the 2015 Scottish Cup, defeating Falkirk 2-1 at Hampden.