The winger trained with the squad this morning before putting pen-to-paper.
The 29-year-old scored in Grimsby Town`s Promotion Final victory over Forest Green Rovers in May.
Arnold was offered a new contract by the Mariners, but after two years at Blundell Park opted to move to pastures new.
Arnold has also played for Mansfield Town, Cambridge United and Alfreton Town and is thought to have been wanted by at least two other National League clubs, but wanted to stay in the area.
Manager Danny Cowley said: “We are delighted to have signed Nathan. It wouldn't have been possible without the crowdfunder. I am so thankful to all of the fans who have contributed. It has allowed us to sign a player that will add real flair and creativity to our squad. Furthermore, Nathan is a fantastic professional and a really good character. We are really looking forward to working with him”.