The 23-year-old will link up with the Cobblers at the beginning of August after the expiry of his contract with Rochdale.
Boothroyd said: "Like our other summer signings, Joe is another player who played a lot of games last season at a higher level than League Two.
"He has a good amount of experience for a player of his age and I am looking forward to working with him.
"We needed a left back in the squad, and we managed to beat a number of clubs to his signature so I am very pleased to welcome Joe to Sixfields."
***Update***Boothroyd has also given a short-term deal to American goalkeeper Neal Kitson with a challenge to impress and earn a longer contract.