The 20-year-old, who has also previously played for Reading and Queens Park Rangers, moved to England from Sweden at the age of 10.
"We're delighted to have had the opportunity to bring in a young prospect of Doug's calibre," Tagg told the club's official website.
"Not only does he have exciting potential for the future but he has already played league football and knows what the game is about at a competitive level.
"He is someone we've looked at the possibility of signing before and we're very pleased we have had the opportunity to add him to our ranks."
A host of Football League clubs had also been monitoring proceedings.