Clark has opted to hang his boots up but will remain at StoneX Stadium as he fills a fresh position, as Saracens' wellbeing and personal development manager.
The 32-year-old has been studying the psychological side of sport and will work closely alongside David Jones, Saracens' head of psychology and personal development.
Clark left Saints in the summer of 2017, having enjoyed a hugely successful spell at Franklin's Gardens after arriving from Leeds in 2010.
He helped the black, green and gold win the Premiership and European Challenge Cup in 2014 and was named player of the season for 2014/15.
But Clark, who won one England cap, is now looking forward to a fresh chapter off the field.
“In terms of being a player I’d say it’s been great to have had the opportunity to come and challenge myself at a club like Saracens," Clark told the Saracens website.
"It hasn’t worked out the way that I had hoped as a player but I have met some great people and learned a lot about myself.
“For my next role, I have been studying hard alongside my rugby career for a number of years.
"I’m passionate abut improving the way in which the mental and emotional health of athletes is approached and handled.
“Thankfully this is an area that Saracens are also looking to improve and I feel very lucky to be continuing as part of the organisation.
"I’d like to thank the club for their support during what has been a particularly difficult period of time for me.
"I look forward to the opportunities and challenges that lie ahead.”
Saracens director of rugby Mark McCall said: “Calum will be working to further the club's personal development and psychology provision.
"Having completed post graduate study in psychology, Calum will be supporting players in various areas such as preparing for a career post-rugby and the mental and emotional aspects of professional sport.
"We are looking forward to Calum starting his new role and helping to progress the Saracens culture."