"We went through the season and I felt that this just feels like it's time to end it and I think it's going to be great for the Cardinals to refresh what's going on here," La Russa said.
La Russa, 67, was with the Cardinals for 16 seasons.
St. Louis defeated the Texas Rangers in the just-concluded seven-game World Series.
"Tony leaves behind a legacy of success that will always be remembered as one of the most successful eras in Cardinals history, team chairman Bill DeWitt Jr. said.
"I knew this day would come. I just hoped that it wouldn't."
La Russa, a four-time Manager of the Year, also managed the
Chicago White Sox (1979-86) and Oakland Athletics (1986-1995).
La Russa had two world titles with the Cardinals and one with Oakland.
St. Louis made a stunning run to this year's championship.
The Cardinals,10 1/2 games out of a playoff berth late in August, got in with a 23-8 run to end the regular season.They then beat Philadelphia, Milwaukee and Texas en route to the title.
"I'm looking forward to what's ahead," La Russa said. "I'm ready to do something different."