"He is an emerging talent who is hungry and determined," said Royals boss Steve Coppell.
"Leroy has great pace and is an excellent finisher who can create something out of nothing. We hope that he can fulfil his potential here.
"His record speaks for itself, and goals were the main thing that let us down last season so we hope he can provide plenty of them.
"This is the biggest signing in the club's history and I would like to commend our chairman for providing the funds to make it possible."