An emotional Shazier posted a video to social media to make the announcement.
"When I was 5 years old, I made the greatest discovery of my life," Shazier, who turned 28 on Sunday, said. "I discovered the game that I love -- the game of football. Ever since then, I've given my life to the game."
Shazier was 25 with a Pro Bowl season behind him on Dec. 4, 2017, when he attempted to make a play against the Cincinnati Bengals and ran headfirst into another player. He collapsed to the ground and was unable to move his legs.
After spinal stabilization surgery and rehab, he regained movement in his legs in February 2018.
"To lose the game in a way I never envisioned has not been easy," Shazier said Wednesday. "When you play the game of football the way I did, you convince yourself you're Superman. That nothing can stop you, but then the moment I got hurt, I stopped being Superman. That was difficult to make sense."
He ends his career with 299 tackles in 46 games (41 starts) to go with seven sacks, seven interceptions and seven forced fumbles.
Shazier, an Ohio State product selected by the Steelers in the first round of the 2014 NFL Draft, was kept on the roster in the 2018-19 seasons and placed on the reserve/retired list earlier this year as a procedural move. He had hoped to play again.
Appreciation for Shazier was quick to follow his announcement.
"A remarkable teammate and an even better person!! I'm glad I was able to play alongside you @RyanShazier," Steelers linebacker T.J. Watt posted to social media.
Shazier said he is stepping away from football, at least for now, to experience other opportunities.
"Football gave me everything I could have ever wanted and more," he said. "It taught me about hard work, dedication, teamwork. It took me to college and the NFL. It made me money and gave me a life most people could only dream about. I'm here today to make sure the world knows how much I still love football, how grateful I am for everything football gave me."
(Field Level Media)