Unger played for 10 seasons, spending the first six with the Seattle Seahawks followed by a four-year stint with the New Orleans Saints.
His retirement is a surprise loss for the 2018 NFC conference finalist Saints. One year remained on Unger's contract, and he was the anchor of an offensive line that allowed quarterback Drew Brees to be sacked just 17 times in 2018.
Unger won a Super Bowl with the Seahawks in 2013, was named an All-Pro in 2012, and was selected to three Pro Bowls, including this past January's event. He was traded to New Orleans, along with a first-round pick, for tight end Jimmy Graham in 2015.
His departure clears $6.9 million in cap space for the Saints, according to ESPN's Mike Triplett.