"He's in absolutely fantastic shape and I'm delighted we've managed to get him," said the Cobblers boss after 29-year-old Carter turned down the offer of a new deal at Cheltenham.
Speaking to BBC Radio Northampton, Carter said that the enthusiasm of the Northampton manager convinced him to come to Sixfields.
"Adie was doing everything to show he was desperate to get me here and I am delighted to have signed."