The one-time England prospect represented the Saxons and made more than 100 appearances for Saracens before joining Newcastle in 2013, for whom he made 19 Premiership appearances.
Saull won the 2010-11 title winning squad and played in the Premiership final against Leicester Tigers.
Saull said: “I am really pleased to have signed for Yorkshire Carnegie.
“I have spoken to Bryan Redpath and Chris Gibson and they set out their vision for the future of the club and their plans to get in to the Aviva Premiership, so it is a very exciting time to be joining the club.
“There are a few players who I know in the Yorkshire Carnegie team, such as James Fitzpatrick and Chris Pilgrim from Newcastle and also I played with Jon Clarke in the Saxons and Charlie Beech and David Doherty for England U20s, so it will be good to work alongside them again.
“I have enjoyed my time at Newcastle, they are a great group of guys and I have made many lifelong friends, but I am now looking forward to the challenge at Yorkshire Carnegie and helping them achieve their ambitions.”