Arizona Cardinals quarterback Carson Palmer announced his retirement Tuesday in a letter on the team's website.
Palmer's announcement comes one day after head coach Bruce Arians retired.
Palmer, 38, was the top pick in the 2003 draft for the Cincinnati Bengals before making his way to Oakland and eventually to Arizona for the final five years of his career.
He led the Cardinals to the NFC Championship Game in 2015 before they fell to the Carolina Panthers.
"Over the years, I've had teammates who decided to hang it up and I would ask them how they knew when it was time to walk away," Palmer wrote. "The answer was almost always the same: You just know.
"For me that time is now. Why? Quite simply, I just know."
Palmer finishes his career with the 12th-most passing yards in NFL history at 46,247. He also ranks 12th in all-time passing touchdowns with 294.
In both categories, he also ranks fourth in Cardinals team history with 16,782 yards and 105 touchdowns.
Palmer missed nine games in 2017 with a broken left arm.
Cardinals backup quarterbacks Blaine Gabbert and Drew Stanton are both free agents, so Palmer's retirement leaves Arizona without a quarterback under contract for the 2018 season.