Palmer was a Heisman Trophy winner at USC and the No. 1-overall pick by Cincinnati in 2002. He threw for 46,247 yards, 11th-most in NFL history, in a career with the Bengals, Oakland and Arizona.
"When I entered the league, I was a 23-year-old kid," Palmer wrote. "I'm leaving a 38-year-old husband and father of four with memories and experiences that I will treasure for the rest of my life. And like most things in life, it feels like it all passed in a blink of an eye."
Acquired by the Cardinals for only a sixth-round pick and a swap of seventh-rounders, Palmer had some of his greatest success in Arizona.
In 2015, he set single-season franchise records for yards passing (4,671) and touchdowns (35) while leading the Cardinals to a 13-3 record, second-best in the NFC. He won his only playoff game that season, in overtime over Green Bay.
Palmer was 46-51 in seven seasons with the Bengals, leading them to the playoffs in 2005 and 2009.
Palmer twice came back from significant knee injuries, one of which came in a playoff game in 2005 vs. the Pittsburgh Steelers.
“My family and I are beyond grateful for everything the game has given us as well as the love and support we’ve felt from fans everywhere we’ve been. That’s been especially true in Arizona, where we never expected to end up but wound up being such a special place for us.”