Leeds will be relegated to the Championship if Worcester beat Cornish Pirates in a two-legged Play-Off this Wednesday and next.
Back, who joined Leeds from Leicester in 2008, led Leeds to promotion to the Premiership in his first year in charge before securing that status with a remarkable second half of season 12 months later.
But the 42-year-old World Cup winner, who became the oldest Test Lion in 2005, feels the time is right to move on and look for a fresh challenge.
"I am very passionate about what I do and I have thrived on the challenge over the past three years, however, taking all things into account, I feel I have taken Leeds as far as I can," said Back.
"The experiences over the last three years have been incredible in terms of my personal and coaching development. I am very proud of what Leeds Carnegie has achieved over the last three years against the odds and I wish Leeds all the success for the future."
Back worked alongside director of rugby and former Leicester Academy and backs coach Andy Key for the majority of his time at Headingley but finished the season working on his own following Key's February sacking.
Victory over Newcastle at Kingston Park gave Leeds real hope of finishing 11th rather than 12th but they eventually missed out because of a worse points difference than their Northern rivals.
Back nearly masterminded a last-gasp escape on the final day of the season but Leeds let a healthy lead over Northampton slip from their grasp when a losing bonus-point would have been to see them stay in the top flight.
"Having met with Neil, he has informed me of his intention to move on at the end of the season to enable him to look for a new challenge," said Leeds chief executive Gary Hetherington.
"I would like to thank Neil for all his efforts during the past three years when he has helped move the club forward into a stronger position.
"In his first season, we won promotion and last season we defied the odds to retain our place in the Premiership. However, this year we have fallen short by the smallest of margins on the final day of the season and that comes as a disappointment to all of us."