The capture of the talented tighthead prop is a major statement of intent from the Blues as they look to build the squad ahead of next season. Further announcements over the make-up of the squad are planned in the coming weeks.
Neath-born Mitchell - who stands 6ft and weighs 18st 8lbs - is a destructive scrummager while his mobility and ball carrying threat around the field also make him a key attacking weapon in the loose.
The 27-year-old started his career at Ospreys, having represented Wales at junior levels and captained his country at Under-19 level, and quickly rose up the ranks to the senior international set-up.
Mitchell made his debut for Wales during the summer tour of North America and Canada in 2009 and was part of the Six Nations squad in 2011 and 2013. He scored his first senior international try against Ireland at the Millennium Stadium in February 2013.
The prop made the move to Exeter Chiefs in the summer of 2011 and has made a total of 35 appearances for the Devon outfit, 25 in the league, and scored one try against Gloucester.
Director of Rugby Phil Davies said: "Craig is an experienced player and he's clearly learnt a lot during his time with Exeter. He's delighted about this opportunity with Blues and we are very excited that a player of his quality and calibre will join us.
"Craig is known for being an exceptional set piece player, but his work rate and impact outside the scrum is also very good. He complements the props we have at Blues and the front row will be much stronger for his signing.
"With a World Cup just around the corner, we are delighted that an international quality player of his experience is coming back to Wales determined to make an impression for us.
"I have spoken to Craig at length about what we expect from him and he's coming here keen to play a big part in the future of the Blues."