The 17-year-old, who has been at Glentoran since he was 10, has joined the Black Cats on a two-and-a-half year deal, subject to international clearance.
Walsh made his senior debut in a County Antrim Shield tie last season before racking up a total of eight appearances for the east Belfast side.
However, he will now hope to follow in the footsteps of Northern Ireland international Trai Hume by working his way into the first-team panel at the Stadium of Light.
Speaking on the club’s official website, Glentoran boss Feeney believes Walsh is now joining a club who has “a great record for developing young players”.
He said: “Obviously I have mixed feelings about losing Rhys as obviously he’s a player who I know would have gone on to do great things for Glentoran as he was already becoming a big favourite here.
“But on the other hand it’s a brilliant opportunity for Rhys as he’s joining a big club with a great record for developing young players and giving them their opportunity. Rhys is a very exciting player who can lift a game with his skill and directness, but he is also a strong and hard-working lad. I’m certain he’ll seize the opportunity and do very well there.
“Rhys is a perfect example of the strength of the Glentoran Academy. We currently have Johnny Russell and Aaron Wightman in the first-team squad, Charlie Lindsay back from Derby County on loan and we have Casey Smyth out on loan to get experience with Dundela.
“Ollie Webber came through the Academy and young Lorcan Donnelly made his debut a couple of weeks ago. Rhys is the latest in a long line of our Academy players who have gone to good clubs in England so it’s a great place for developing young players.”
Sunderland Academy Robin Nicholls acknowledged they have tracked Walsh’s progress for some time.
“Rhys is a player we have coveted for some time and he spent a period with us on trial earlier in 2023,” he told Sunderland’s official website.
