The 22-year old English-born once-capped Scotland international has signed a three-and-a-half-year deal for an undisclosed fee with the Robins which has delighted manager Derek McInnes.
"He has amassed quite a lot of Under-21 games for Scotland and is now involved in the full senior squad as well.
"He is 22 years of age and that is a good age for us, which is important. We think we have got a very good deal for the club, considering he only had six months of his contract left and a few other clubs were looking at him.
"Liam is someone we think will only get better. He gets around the pitch, utilises the ball well and takes responsibility for his position."