The 25-year-old, who has spent the past five years at Northampton Town has penned a one-year deal at Huish Park.
Plymouth born Ben started his career at Swindon Town before joining Newcastle United. After two seasons at Newcastle he joined The Cobblers, where he made over 170 appearances.
Manager Paul Sturrock said: "I worked with Ben when I was at Swindon Town, before he joined Newcastle United, he was a centre back at that time.
“I feel Ben’s career over the past few seasons has stagnated in a way that he has become a utility player and played in about five different positions.
"I would like to settle him down now into playing in just two positions. He has all attributes to be a great signing for the club and I am looking forward to working with him."