The former England skipper will call an end to his 16-year playing career with a number of achievements under his belt, one of which is leading his side to the Premiership title in 2011.
"Very few players have the chance to retire on their own terms," Borthwick told the club's official website.
"Saracens did ask me if I'd like to carry on but I feel that the time is right for me to finish playing at the end of the season. That's still a few months away, and I am obviously 100% focused on improving as a player and leading this team to the best of my ability."
The 34-year-old has made 253 Premiership appearances.