Foster, 24, spent last term at Clifton Lane having previously played with Newcastle Falcons and Blaydon RFC. He made his Premiership debut for hometown club, Newcastle, against Saracens in April 2015 and featured in the European Rugby Challenge Cup against Brive at the start of 2016.
“It is going to be a good opportunity for me at Carnegie and I’m excited to get in and work hard with the boys to see how high we can finish,” said Foster on his move.
“It was a tough last season with Rotherham but a massive learning curve and a chance for me to play at the next level up.
“I had a good experience in the Academy at Newcastle but this year has exposed me to senior rugby and I have learnt a lot from that. It was a test of character as well; going in on a Monday morning’s been hard at times but you must learn mentally as a professional player to keep going. Hopefully I can put that experience to good use now.
“As a front-row, the Championship is a great place to learn your game but it is a tough learning curve. I’d recommend playing in the Championship to any academy player so you can play as much rugby as you can and get your chance to step up and learn your trade.
“I am very excited to be working with Jimmy Lowes and Steve Boden and this is an opportunity to learn as much as I can.”