A third-year NFL player, he spent 2011 and 2012 with the New York Jets.
In his tweet, McElroy, 25, thanked coach Marvin Lewis and owner Mike Brown and his family for giving him the opportunity to play in Cincinnati.
"The fans make this decision especially difficult, as you have provided so much joy throughout my career," the tweet continued. "Playing in the NFL was my lifelong dream; therefore, I must also thank the New York Jets for providing me with my original opportunity."
McElroy was drafted by the Jets in the seventh round in 2011. He appeared in two games for them in 2012, the second of which he lost to San Diego. For his career, McElroy was 19-for-31 passing for 214 yards and one touchdown and one interception.
Signed to a futures contract in Cincinnati at the end of last season, the former Alabama standout had been expected to give the Bengals another quarterback to get work in during training camp behind backups Josh Johnson and Zac Robinson. When nine-year veteran Jason Campbell was signed Thursday, the Bengals became that much deeper at the position. Campbell will now slip into the No. 2 quarterback spot behind starter Andy Dalton.
At this time, I would like to announce my retirement from the NFL. pic.twitter.com/b9cUHLPj70
— Greg McElroy (@GVMcElroy) March 21, 2014