Hicks, 23, was diagnosed in high school with Type 1 diabetes.
Hicks, who routinely tops 100 mph, is recovering from Tommy John surgery on June 26, 2019. The right-hander's availability for this season was uncertain.
In a statement posted to Twitter, Hicks said he looks forward to playing in 2021 and using his platform to raise awareness for the diabetic community.
2020 Season❗️❗️❗️ pic.twitter.com/zxLiq7d7Gc— Jordan Hicks (@Jhicks007) July 13, 2020
Hicks had been taking part in workouts at Busch Stadium, leading up to the Cardinals' opener on July 24 at home against Pittsburgh.
"We respect and understand Jordan's decision to opt out this season," Cardinals president of baseball operations John Mozeliak said. "We wish him well as he continues his recovery from elbow surgery, and we look forward to seeing Jordan back on the mound for the 2021 season."
Dodgers pitcher David Price, Giants catcher Buster Posey and Nationals infielder Ryan Zimmerman are among about a dozen players who have opted out this year.
Hicks was 2-2 with 14 saves and a 3.14 ERA last season before he injured his elbow. He has hit 105 mph with his fastball.
Hicks was due $214,370 as a prorated share of his $578,800 salary. He gets paid if the preexisting health concern has been determined to make him a high-risk individual.
Carlos Martinez led St. Louis with 24 saves last season, posting his first save on June 1. The Cardinals had been working in spring training in February to move Martinez to the rotation, where he was a two-time All-Star.
The Associated Press contributed to this report.