O’Reilly arrives at the back off the back of an impressive campaign with Crewe Alexandra in League Two, where he was named as the Railwaymen’s Player of the Season after registering seven goals and 14 assists in 2025-26.
The 22-year-old previously gained loan experience at Shrewsbury Town and MK Dons during the previous season, while also making his senior Villa bow against HŠK Zrinjski in the UEFA Europa Conference League in December 2023.
Boss Grant McCann said: "Tommi is a really good signing for us, what we like about him is his directness, his ability to drive and take people on, and he's a really tough kid. He can take the hits and he gets up and keeps going.
Latest Doncaster Rovers signing Tommi O'Reilly. Picture courtesy of DRFC.placeholder image
Latest Doncaster Rovers signing Tommi O'Reilly. Picture courtesy of DRFC.
"He played every game for Crewe last season and produced 21 goal contributions. We are delighted to have such an exciting talent added to our squad."
O'Reilly added: "I'm delighted to be here and hopefully I can hit the ground running. I think this a brilliant next step for me in my career.
"I had a few conversations with the manager before joining, he was really honest and I liked what he said. He spoke very highly of the club, what he expects of me and how I can impact the team. That had a big influence on my decision.
"I'm a creative player and I like to get on the ball and work hard for the team. I want to beat my man and create goals. I just want to help the team."