Maddux, 42, was a four-time Cy Young Award winner and eight-time All-Star over his career that started in 1986 with the Chicago Cubs and included stints with Atlanta, Los Angeles and San Diego.
"I'm very proud of what I did on the baseball field, but I'd like to think I'm the same person I was 20 years ago," Maddux said.
His 355 victories are eighth most in major-league history. He had 17 consecutive seasons in which he won at least 15 games.
Maddux is 10th on the all-time strike list (3,371) and is fourth in games started (740) and 13th in innings pitched (5,008 1/3).
"I'm just here to say thank you to everyone in baseball," Maddux said. "It's going to be hard walking away from baseball, but it's time ...
"I'll miss all of it. I'll miss the game, hitting, pitching, hanging out with the guys, standing at home plate wondering what pitch is coming. The plane rides are fun, playing golf on the road is fun, playing poker with the guys ... spring training is always fun, it's where you get to work on baseball stuff."