The 32-year-old only joined Vale earlier this summer following a two-year stint with Crewe Alexandra.
However, the defender refused the offer of a revised contract at Vale Park after it had emerged that the club had failed to exit administration.
That news alerted Northampton boss Aidy Boothroyd, who has tied the centre-back down to a two-year contract.
"In David we are talking about the man who lifted the play off trophy at Wembley a couple of months ago," Boothroyd told the club's official website. "He had the chance to move to a club on his doorstep in Port Vale and he took it.
"Things didn't work out there but we tried to bring David in earlier this summer, it didn't happen then but now we have got a lucky break. I sold the club to David and fortunately he has brought in to what we are trying to do.
"He is a senior figure, a leader, he has been promoted three times. He is great in the dressing room and he is a voice on the pitch. He knows this level inside out and I think he is the voice who will connect us together and give the whole club a lift."
Artell began his career with Rotherham United.