Tagicakibau, who has five caps for Fiji, made 43 appearances for Saracens during a three-year spell from 2009 to 2012.
"I've really enjoyed the year in Bristol, but I am excited to be returning to Saracens," Tagicakibau told Saracens' official website.
"The squad is going well and Allianz Park looks a special place to play rugby. I'm looking forward to helping the club move forward."
Saracens are currently top of the Aviva Premiership table, while Bristol are in the Championship.