The 26-year old goalkeeper has joined on an initial one-year deal as a free agent after leaving Cardiff City earlier this summer.
Robins boss Derek McInnes has had the former Manchester United, Royal Antwerp and QPR gloveman with the squad during the pre-season training camp in Spain and is now thrilled to add him to the squad proper.
"We have been in discussions with him and his agent for a long time, always keeping an eye on his situation," McInnes told the club's official website.
"We've had various potential goalkeepers on our list and it seemed like Tom had agreed a deal elsewhere.
"In the end, he agreed to come on trial with us and the time he spent in Spain with Nigel Spink (goalkeeping coach) has shown his potential. He is a good age and a good talker, as well as being mature and very confident."