The 17-year-old has put pen to paper on a professional contract with the Old Gold club.
O’Donnell has come in from Derry City, where he has already been playing senior football.
A former Cockhill Celtic youth, O’Donnell has also played for Ireland’s Under-17s.
Academy manager for football, Jon Hunter-Barrett, stated: “Luke’s a boy we tried to sign a year ago so it’s been a real challenge for us but, most importantly, for Luke and his family to wait for this amount of time before officially signing for us.
“He’s another versatile player who can play as a six, eight or even as a center back, which he’s shown he can do for his national team.
“Luke’s a great height and shape, and an athletic mover who can manage the ball. He’s another solid personality, someone who is consistent every day and we feel we can build a development block that’s going to be needed for him to sustain a career in the game moving forward.”