The 22-year-old right winger, a readymade replacement for the released JP McGovern has made over 115 appearances for The Dons and Paul Sturrock has been tracking him for a long time.
A former player's player of the year at the National Hockey Stadium, Small brings pace and versatility to the club after a 'six-figure' nominal fee was agreed and will officially join the club on June 1.
Sturrock told Wednesday's official site: "I watched him from afar when I was at Plymouth and although he had a few niggling injuries last season I am very excited about him. He has got great potential and we need to bring these young, keen, enthusiastic players to the club.
"With Drew missing, we've laced a bit of pace through the middle so we have been screaming out for that type of player. He's also played wide-left a lot which gives me a dual purpose player."
Sturrock wants a few other faces into the club before June - when he takes a well-deserved break.