Tarpley, 23, announced his decision in an Instagram post Wednesday evening:
The only thing comforting about not knowing this play would be the last of my career, is knowing that I never took a second for granted. After months of introspection, I am retiring from football. I suffered the 3rd and 4th concussions of my career this past season and I am walking away from the game I love to preserve my future health. This decision is the hardest I've made yet but after much research and contemplation I believe it's what is best for me going forward. I'd like to extend my gratitude to everyone that helped me along the way. Thank you to my coaches at Wayzata and Stanford, and to lifelong friends that I was blessed to call teammates. You all molded me into the man I am today. To my family, I'll never be able to repay your unwavering support and love, I just hope that I can continue to show how gracious I am and make you proud. I also want to thank the Buffalo Bills organization, coaches, and teammates for helping me fulfill my lifelong dream in the NFL. Last but not least, I'm proud to be a part of #BillsMafia and playing in front of the best fans in the league is something I won't forget. Thank you God for all that you have blessed me 🙏. I'm excited for my future.
"After months of introspection, I am retiring from football," Tarpley wrote. "I suffered the 3rd and 4th concussions of my career this past season and I am walking away from the game I love to preserve my future health.
"This decision is the hardest I've made yet but after much research and contemplation I believe it's what is best for me going forward."
Tarpley earned $416,912 last season with the Bills. In retiring, he loses the potential to earn a non-guaranteed $525,000 base salary this season.
"A.J. Tarpley has spoken with Rex Ryan and indicated that he plans to retire, but we are unaware at this point as to whether A.J. has formally submitted the necessary paperwork to the league. He has expressed how difficult this decision was and we certainly respect his decision," the Bills said in a statement.
"We enjoyed having A.J. as a valued member of our team last year and wish him the best of luck in his future endeavors."
Tarpley is the latest NFL player to announce an early retirement because of concussions or other long-term health concerns. Former San Francisco 49ers linebacker Chris Borland ended his career last year at age 24, also because of concussions.
"I just honestly want to do what's best for my health," Borland told Outside the Lines in March 2015. "From what I've researched and what I've experienced, I don't think it's worth the risk."
Tarpley, a California native who attended Stanford, earned a spot on the Bills' 53-man roster last season as an undrafted free agent. He played in 14 games, mostly on special teams. He started the final two games of the season and recorded an interception in each game.
His game-sealing, fourth-quarter interception of Jets quarterback Ryan Fitzpatrick in last season's finale, pictured in his Instagram post, was the final play of his career.