The 24 year-old former Moseley and Worcester Academy player has signed a one contract with the club.
He has featured in the majority of Coventry’s National League One fixtures this season and has amassed over 50 points. He was also named Man of the Match in Coventry’s 27-10 victory over Mowden Park in April.
Mowden Park coach Garry Law said of his arrival: “We are very happy that Caolan has agreed to join us for season 2016/17.
“He has played championship rugby at both 10 and 15 which will be an asset we hope to use.
“We had an eye on Caolan, and our recent fixture against Coventry only underlined our thoughts.
“It's an exciting time just now with the squad taking shape for next season and we see Caolan playing a massive part in what we hope to achieve both on and off the pitch.”
Ryan said ahead of his move: "I'm very excited to be joining Darlington Mowden Park for next season.
"It's an ambitious club and I'm looking forward to being part of a strong squad.
"I'am going to work hard for Danny John and Garry, and hopefully achieve lots for the great support at the Northern Echo Arena."