The 25-year-old spent three years at Northampton and was named the club's Young Player of the Year in 2004/05.
A former England Under 18 international, Jones will compete for the number nine shirt at Sixways with Matt Powell, Ryan Powell and Jonny Arr.
"Ben is an exciting young prospect who has played very well for a number of seasons in National Division One," said Director of Rugby Mike Ruddock.
"Clive Griffiths was particularly impressed with him during his time at Doncaster Knights and if he turns out to show the same pedigree that Netani Talei has shown then we will be very pleased with his signing.
"Having looked at his game he seems to be the sort of scrum half that could really blossom under the proposed ELVs when we expect the ball to be in play for longer periods in matches. There will be more room to make ground, particularly on scrums where the defence now has to stand five metres behind the scrum.
"People might ask why we need another scrum half when we have some exceptional quality in Matt Powell, Ryan Powell and Jonny Arr.
"But in a singular position, like scrum half or hooker, it's imperative to have cover, depth and options, particularly as we play in three major competitions and we also run an A team. We look forward to Ben becoming a Warrior and making an impact."