Melvin, who signed a one-year contract worth $1.75 million in March, was expected to compete with third-year player Tre Herndon to start opposite rookie first-round pick C.J. Henderson. He had been at the team facility all week and told the team of his decision on Thursday.
The 30-year-old Melvin has four interceptions and 41 pass breakups in seven seasons with Baltimore, Indianapolis, Detroit, New England and Oakland.
Nose tackle Al Woods and linebacker/defensive end Lerentee McCray also have opted out of the 2020 season. Woods was signed to shore up a run defense that gave up 139 yards per game last season. McCray is a core special-teams player who could fill in on defense.