Currently sidelined with a dislocated shoulder sustained whilst playing for Wales against Ireland in this season's Six Nations, Mitchell says the time was now right for him to leave the Ospreys.
"I'm really looking forward to it," said Neath-born Mitchell, who has won eight caps for his country.
"It's going to be a fresh start for me and a move that is right for me and my career at this stage. I've had six good years with the Ospreys, but I felt the time was right to try something else and signing for Exeter is a great opportunity for me.
"Yeah, it's going to be my first crack at English rugby and the Premiership. I've spoken to a few boys about it and they've said it's tough, but that it is also a very good standard. Obviously I've come up against English sides before with the Ospreys and with Wales, so I know a little bit about the players and the teams.
"I was very impressed when I came down and looked at the place.
"Obviously the facilities are first class and I had a decent chat with Rob [Baxter] about the club and what they want to do in the future. As I said, it's a fresh start for me and one that I think will help move my career forward. I know one or two of the boys already, like Phil Dollman, so it should exciting for me when I move down."
One man delighted to welcome Mitchell on board is coach Baxter, who has monitored the progress of the Welsh forward for a number of months.
"We've had Craig lined up for a while, but with the Six Nations going on he asked us to keep things under wraps for a while so that's what we did," said the Exeter chief.
"It's great to have him on board. It's unfortunate for him that he picked up the injury pretty late in the Six Nations but I think everyone who watched him will think he's done very well, he's certainly proved a few points and certainly progressed his international credentials.
"I'm really looking forward to starting to work with him, he's a nice down-to-earth guy, I think he's looking forward to coming to Exeter and battling to be playing plenty of Premiership rugby. Hopefully we can help him continue with his international ambitions, as we'd like to with some of our other players.
"I think he's a really good signing for us and anybody who saw the internationals will know he's a quality guy who works hard and that's the kind of player we like - we don't like guys who just wander around. I'm really pleased we've got him and he strengthens a really important area. I think we've got a scrum that's improving all the time, our props are playing really well, but you can never have too many quality guys there. He's also a very good age as well, so he'll keep improving and developing and I think we're looking forward to seeing how he goes over the next couple of years."