Banks has put pen to paper on a deal which ties him to the club until the end of next season.
The 20-year-old, who was released by Rotherham United at the end of the 2011/12 season, has been playing non-league football since leaving the Millers.
He is delighted to be making a return to the Football League with Chesterfield, saying: "I can't tell you how happy I am after two years out of the professional game. It's a very exciting time to be joining Chesterfield with the club at the top of the table."
Commenting on the signing, assistant-manager Leam Richardson said: "He's a young lad we've identified as a very good prospect. We expect him to go on and make the first-team breakthrough and be a big part of what we're trying to do."
Prior to joining FC United of Manchester, Banks had spells with North Ferriby, Scarborough Athletic and Gainsborough Trinity.
He is the son of Ian Banks, who was Chesterfield's assistant-manager under Nicky Law.